Adding MSELoss for regression tasks in HubertForSequenceClassification model
Author: aroun-coumar
Pull request: yes

# What does this PR do?

Fixes [#33500 ](https://github.com/huggingface/transformers/issues/33500)
<!--
Congratulations! You've made it this far! You're not quite done yet though.

Once merged, your PR is going to appear in the release notes with the title you set, so make sure it's a great title that fully reflects the extent of your awesome contribution.

Then, please replace this with a description of the change and which issue is fixed (if applicable). Please also include relevant motivation and context. List any dependencies (if any) that are required for this change.

Once you're done, someone will review your PR shortly (see the section "Who can review?" below to tag some potential reviewers). They may suggest changes to make the code even better. If no one reviewed your PR after a week has passed, don't hesitate to post a new comment @-mentioning the same persons---sometimes notifications get lost.
-->

<!-- Remove if not applicable -->



## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

@ylacombe
@eustlb

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker
- vision models: @amyeroberts, @qubvel
- speech models: @ylacombe, @eustlb
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @zucchini-nlp (visual-language models) or @gante (all others)
- pipelines: @Rocketknight1
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @SunMarc
- chat templates: @Rocketknight1

Integrations:

- deepspeed: HF Trainer/Accelerate: @muellerzr
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc

Documentation: @stevhliu

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
- TensorFlow: @Rocketknight1

 -->


Comments:
Any news on this PR? 

Gentle ping @ylacombe !

I haven't realized, but as you can see with the failing `check_repository_consistency`, the model copies some code from `Wav2Vec2ForSequenceClassification`, which you also have to modify!

You then need to pass on the changes to all models copying `Wav2Vec2ForSequenceClassification` by doing `make fix-copies`!
We do that to ensure consistency of the repository. That way, your fix will be apply to a lot of audio models as well!

Hey @ylacombe  i am stuck with this error. Please help me.
Thanks!

```
(myvenv)
Arun kumar@LAPTOP-0U925LO8 MINGW64 ~/OneDrive/desktop/Transformers/transformers (fix-classification-loss)
$ make fix-copies
python utils/check_copies.py --fix_and_overwrite
Detected changes, rewriting src/transformers\models\hubert\modeling_hubert.py.
python utils/check_modular_conversion.py  --fix_and_overwrite
Traceback (most recent call last):
  File "C:\Users\Arun kumar\OneDrive\desktop\Transformers\transformers\utils\check_modular_conversion.py", line 73, in <module>
    non_matching_files += compare_files(modular_file_path, args.fix_and_overwrite)
  File "C:\Users\Arun kumar\OneDrive\desktop\Transformers\transformers\utils\check_modular_conversion.py", line 53, in compare_files
    generated_modeling_content = convert_modular_file(modular_file_path)
  File "C:\Users\Arun kumar\OneDrive\desktop\Transformers\transformers\utils\modular_model_converter.py", line 1136, in convert_modular_file
    code = file.read()
  File "C:\Users\Arun kumar\AppData\Local\Programs\Python\Python39\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 1699: character maps to <undefined>
make: *** [Makefile:84: fix-copies] Error 1
```
 

Is this my local setup problem?
 

cc also @eustlb

Hey @aroun-coumar, sorry for the late response!

I think you first need to modify `Wav2Vec2ForSequenceClassification` with the same modif you've made for Hubert. Then you should be able to run `make fix-copies` without any issues!

Let me know if that helps / works!