Update InstantStyle usage in IP-Adapter documentation

[JY-Joy]

What does this PR do?

Update correct InstantStyle usage in IP-Adapter documentation, as mentioned in #7668

Before submitting

• [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [x] Did you read the contributor guideline?
• [x] Did you read our philosophy doc (important for complex PRs)?
• [x] Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• [x] 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?

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