[BugFix] Fix initialization of draft model. (#29319)

Signed-off-by: Andrey Khalyavin <halyavin@yandex-team.ru>
Signed-off-by: Tyler Michael Smith <tlrmchlsmth@gmail.com>
Co-authored-by: Tyler Michael Smith <tlrmchlsmth@gmail.com>

vllm/v1/worker/gpu_model_runner.py

@@ -3460,6 +3460,10 @@ class GPUModelRunner(
             scope="local",
         )
         prepare_communication_buffer_for_model(self.model)
+        if (drafter := getattr(self, "drafter", None)) and (
+            drafter_model := getattr(drafter, "model", None)
+        ):
+            prepare_communication_buffer_for_model(drafter_model)
         mm_config = self.model_config.multimodal_config
         self.is_multimodal_pruning_enabled = (
             supports_multimodal_pruning(self.get_model())