[Attention] Add missing kv cache scale setup

[MatthewBonanni]

Purpose

#25103 missed the kv cache scale setup when breaking out MLAAttention. This PR adds this to MLAAttention.__init__

cc @pavanimajety

Test Plan

Test Result

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[gemini-code-assist]

Code Review

This pull request correctly adds the missing KV cache scale and quantization setup to the MLAAttention layer. The implementation appears to be a direct copy of the logic from the Attention layer. While this fixes the immediate issue, it introduces significant code duplication. My review includes a suggestion to refactor this common initialization logic into a shared helper function to improve maintainability and avoid potential inconsistencies in the future.

[pavanimajety]

LGTM, thanks for the quick fix!