### What this PR does / why we need it?
Corrects the attribute access for retrieving the device from `q_a_proj`
to `q_proj`. This prevents an `AttributeError` as `q_a_proj` does not
exist on the class instance.
### Does this PR introduce _any_ user-facing change?
None.
### How was this patch tested?
Need MLAPO tests.
- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0
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Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>
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