[Docs] Add return annotation to fused_mm_input_norm_triton (#58687)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

vllm/model_executor/layers/fusion/mm_input_norm.py

@@ -71,7 +71,7 @@ def fused_mm_input_norm_triton(
     outputs: torch.Tensor,
     weight: torch.Tensor,
     bias: torch.Tensor,
-):
+) -> torch.Tensor:
     """Fused per-channel affine transform for normalisation.
 
     Args: