Fixed issue where ACCELERATE_USE_CPU="False" results in bool(True)
Author: madhavajay
Pull request: yes

- This results in cpu mode on Apple Silicon mps

# What does this PR do?
Fixes a bug which prevents device("mps") working if `ACCELERATE_USE_CPU` is set to anything including "False".

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Fixes # (issue)


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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24907). All of your documentation changes will be reflected on that endpoint.