fix variable undefined bug when return_tensors is not specified in llava processing
Author: chenweize1998
Pull request: yes



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Fixes #34952  (issue)


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Comments:
Just revised the code according to the review. 

Core maintainer's approve and we'll merge it!

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_34953). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.