Fix mps device check for moe histogram routing

[belamaran96-coder]

What does this PR do?

Fixes #45685

This PR updates the device check during the histogram calculation in the MoE routing logic (moe.py and finegrained_fp8.py).

Apple Silicon (mps) does not support histc for integer types, so it must be cast to a float before the operation, aligning it with the CPU behavior.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Who can review?

cc @amyeroberts (as discussed in the issue)

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