fix loss scaling only when compute_loss_func is used
Author: BlackNoodle
Pull request: yes

# What does this PR do?

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In [#34198](https://github.com/huggingface/transformers/commit/6ba31a8a94bf7cfeaf59ffc3bc9e0b0cd3e25788#diff-ed55888e6665791fe92cc8fc0c499da54f4ace6738551cd9a2591881cda076deR3629), the line `loss *= self.args.gradient_accumulation_steps` was introduced due to `Negate accelerate grad accum div`. This change was made to correct errors encountered during gradient accumulation. However, the scaling should only occur when compute_loss_func is used, so the code was modified accordingly.


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Comments:
This will conflict with https://github.com/huggingface/transformers/pull/34373, however the correct version of this is either if `compute_loss_func` is used **or** `self.model_accepts_loss_kwargs is True`