[Feat] Adapted mtp function to Qwen3-next (#3918)

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

Adapts mtp function to Qwen3-next.

- vLLM version: v0.11.0
- vLLM main:
83f478bb19

Signed-off-by: drslark <slarksblood@qq.com>

vllm_ascend/spec_decode/__init__.py

@@ -29,9 +29,9 @@ def get_spec_decode_method(method,
                            is_torchair_graph=False):
     if method == "ngram":
         return NgramProposer(vllm_config, device, runner)
-    elif method in ["eagle", "eagle3"]:
+    elif method in ("eagle", "eagle3"):
         return EagleProposer(vllm_config, device, runner)
-    elif method == 'deepseek_mtp':
+    elif method in ('deepseek_mtp', 'qwen3_next_mtp'):
         if is_torchair_graph:
             return TorchairMtpProposer(vllm_config, device, runner)
         return MtpProposer(vllm_config, device, runner)