Fixed nll with label_smoothing to just nll
Author: nileshkokane01
Pull request: yes

# What does this PR do?

This PR fixes #28167 by making label_smoothing= 0 . 
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Fixes #28167


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@younesbelkada 

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Comments:
@younesbelkada ,
Can you please review the changes? 

@younesbelkada  ,
I rebased and resolved the conflict. I hope its a right way, or else let me know.

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_28708). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

cc @younesbelkada 

@ArthurZucker IMO this is not really breaking, it is even the opposite as it fixes some subtle bugs with respect to training with BLIP- see @NielsRogge ' comment here: https://github.com/huggingface/transformers/issues/28167#issuecomment-1867398976

thinking a bit about it, indeed maybe we should make that configurable through a variable in the config so that potentially users could revert to original behaviour if needed. 
@nileshkokane01 would be happy to adjust the PR accordingly? You just need to add a new variable `label_smoothing` in the blip config class and set it to 0

@younesbelkada sure! I'll do that.

thank you @nileshkokane01 !

@younesbelkada ,

Do I have to change the nll loss to the following as well: 

`
loss_fct = CrossEntropyLoss(reduction=reduction, label_smoothing=self.config.lable_smoothing)`

hi @nileshkokane01 
Yes please, this sounds great

@younesbelkada ,
can you have a look ?