[Fix Bugs] Fix keys in `_load_pretrained_model`
Author: hanrui1sensetime
Pull request: yes

# What does this PR do?

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Fixes the bug when `_load_pretrained_model`.
`f'{prefix}.key'` is wrong because the variable `key` is not used is this branch case.
And this bug will lead to load some models failed like BLOOM-176B.


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

cc @sgugger