Change audio kwarg to images in TROCR processor

[ydshieh]

What does this PR do?

Fix a bug in TROCR processor introduced in #18325

Currently, we have failed job run with error

        if audio is None and text is None:
>           raise ValueError("You need to specify either an `audio` or `text` input to process.")
E           ValueError: You need to specify either an `audio` or `text` input to process.

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks a lot for fixing my mess! Bad copy-paste from the speech to text models 😬