[peft] simple update when unscale

[sweetcocoa]

What does this PR do?

In peft's unscale, it unnecessarily traverses modules even when weight is None.

I think a modification like this PR would logically achieve the same behavior without traversing.

It seems like a simple fix, but please review.

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• PEFT: @sayakpaul @BenjaminBossan

[HuggingFaceDocBuilderDev]

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[BenjaminBossan]

This should achieve the same result while avoiding unnecessary iteration. Thanks!

[sayakpaul]

Thanks for your contributions!