[Model] Add SupportsMultiModal.get_language_model interface (#16007)

Signed-off-by: NickLucche <nlucches@redhat.com>

vllm/model_executor/models/phi4mm.py

@@ -1802,3 +1802,6 @@ class Phi4MMForCausalLM(nn.Module, SupportsLoRA, SupportsMultiModal,
             connector=["audio_projection_for_vision", "audio_projection"],
             tower_model=["vision_encoder", "embed_tokens_extend"],
         )
+
+    def get_language_model(self) -> torch.nn.Module:
+        return self.model