Fix fsdp2 example typo

[shimizust]

What does this PR do?

• Fix typo in the fsdp2-fp8 example

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  Pull Request section?
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• Did you make sure to update the documentation with your changes? Here are the
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  here are tips on formatting docstrings.
• Did you write any new necessary tests?

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Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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@SunMarc @zach-huggingface

[S1ro1]

Thank you!

[HuggingFaceDocBuilderDev]

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