[Hybrid][torch.compile] Refactor mamba2 forward to avoid obscuring linear projections under custom op (#28587)

Signed-off-by: Tomer Asida <57313761+tomeras91@users.noreply.github.com>

vllm/model_executor/models/mamba2.py

@@ -87,8 +87,7 @@ class Mamba2DecoderLayer(nn.Module):
         else:
             hidden_states, residual = self.norm(hidden_states, residual)
 
-        output = torch.empty_like(hidden_states)
-        self.mixer(hidden_states, output)
+        output = self.mixer(hidden_states)
         return output, residual