[Minor] Fix minor mistake in docstring of replace_pattern (pytorch#147611)

Fixes pytorch#147610

Pull Request resolved: pytorch#147611
Approved by: https://github.com/soulitzer

Author: xwu99

torch/fx/subgraph_rewriter.py

@@ -140,7 +140,7 @@ def forward(self, x, w1, w2):
 
 
         def pattern(w1, w2):
-            return torch.cat([w1, w2]).sum()
+            return torch.cat([w1, w2])
 
 
         def replacement(w1, w2):