Indexing fix - CLIP checkpoint conversion
# What does this PR do?

In the conversion script, there was an indexing error, where the image and text logits where taken as the 2nd and 3rd outputs  of the HF model. However, this is only the case if the model returns a loss. 

This PR updates the script to explicitly take the named parameters. 

Fixes #22739


## Before submitting
- [ ] 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](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? 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](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?
_The documentation is not available anymore as the PR was closed or merged._