[Bugfix] Fix DP MTP Dummy Run (#35243)

Signed-off-by: Benjamin Chislett <bchislett@nvidia.com>

vllm/v1/worker/gpu_worker.py

@@ -903,7 +903,8 @@ class Worker(WorkerBase):
             self.profiler.stop()
 
     def execute_dummy_batch(self) -> None:
-        self.model_runner._dummy_run(1, uniform_decode=True)
+        num_tokens = getattr(self.model_runner, "uniform_decode_query_len", 1)
+        self.model_runner._dummy_run(num_tokens, uniform_decode=True)
 
     def add_lora(self, lora_request: LoRARequest) -> bool:
         return self.model_runner.add_lora(lora_request)