fix chunked prefill implementation issue-43082

[marcndo]

What does this PR do?

Fixes #43082

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the [contributor guideline] (https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request),
  Pull Request section? Yes
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case. chunked prefill implementation is incorrect #43082
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings. N/A
• Did you write any new necessary tests? N/A

Who can review?

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.

[zucchini-nlp]

Thanks, can you mark PR as ready for review?

[marcndo]

Sure, I just did so.

[HuggingFaceDocBuilderDev]

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