[UT] Fix test_mla_v1 ut test

[zhangxinyuehfad]

What this PR does / why we need it?

Fix test_mla_v1 ut test

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[github-actions]

👋 Hi! Thank you for contributing to the vLLM Ascend project. The following points will speed up your PR merge:‌‌

• A PR should do only one thing, smaller PRs enable faster reviews.
• Every PR should include unit tests and end-to-end tests ‌to ensure it works and is not broken by other future PRs.
• Write the commit message by fulfilling the PR description to help reviewer and future developers understand.

If CI fails, you can run linting and testing checks locally according Contributing and Testing.

[gemini-code-assist]

Code Review

This pull request fixes a unit test test_mla_v1 by mocking NPU-specific calls, allowing the test to run in a CPU-only environment. The changes are correct, but there is significant code duplication between two test methods. I've suggested refactoring this duplicated logic into the setUp method to improve maintainability and prevent future bugs.