[docstring] fix docstring DPRConfig
Author: AVAniketh0905
Pull request: yes

# What does this PR do?

Fixes #26638 only for `DPRConfig`

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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_26674). All of your documentation changes will be reflected on that endpoint.

> Thank you!

Thank you very much!!!