[Misc] Add extra checking to torchair_graph_config. (#1939)

### What this PR does / why we need it?

cherry-pick #1675  to main
This PR adds validation checking to torchair_graph_config for better
reliability.

Co-authored-by: whx-sjtu <2952154980@qq.com>

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?


- vLLM version: v0.10.0
- vLLM main:
2836dd73f1

Signed-off-by: 22dimensions <waitingwind@foxmail.com>

vllm_ascend/models/deepseek_v2.py

@@ -313,7 +313,8 @@ class CustomDeepseekV2MoE(nn.Module):
         ascend_config = get_ascend_config()
         self.torchair_graph_enabled = ascend_config.torchair_graph_config.enabled
         self.enable_multistream_moe = \
-            ascend_config.torchair_graph_config.enable_multistream_moe
+            ascend_config.torchair_graph_config.enable_multistream_moe and \
+            self.torchair_graph_enabled
 
         self.gate = ReplicatedLinear(config.hidden_size,
                                      config.n_routed_experts,