[Fix] Fixes attribute error in MLA implementation (#3618)

### 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

---------

Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>

vllm_ascend/attention/mla_v1.py

@@ -737,7 +737,7 @@ class AscendMLAImpl(MLAAttentionImpl):
         self.qb_qt_bias = qb_qt_bias.reshape(
             self.num_heads * (self.qk_nope_head_dim + self.qk_rope_head_dim))
 
-        device = self.q_a_proj.weight.device
+        device = self.q_proj.weight.device
         self.gamma1 = self.q_a_layernorm.weight.data
         self.beta1 = self.q_a_layernorm.bias.data
         self.gamma2 = self.kv_a_layernorm.weight.data