fix a small bug in sdxl

[xiaohu2015]

fix a bug

What does this PR do?

Fixes # (issue)

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?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a Github issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

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.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[pcuenca]

I think this is correct!

We may have to correct the same in pipeline_stable_diffusion_upscale.py cc @patrickvonplaten @sayakpaul @williamberman

[pcuenca]

Just one thing, @xiaohu2015, could you please run "make style" in your checkout to format the files? If you can't, let us know and I'll do it.

[xiaohu2015]

Just one thing, @xiaohu2015, could you please run "make style" in your checkout to format the files? If you can't, let us know and I'll do it.

thanks, you can help do that

[pcuenca]

Thanks @xiaohu2015 for your contribution! Merged in #4019 :)