save full_osd in fsdp mode
Fixes a typo in which the variable full_osd is referenced before definition if run in fsdp mode. The fix allows model files to be saved when running in fsdp.

Links to issue: https://github.com/huggingface/transformers/issues/24057

Fixes # 24057

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24328). All of your documentation changes will be reflected on that endpoint.<|||||>Hello, PR #24446 addresses this issue. <|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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