Don't call erase if node is already erased in batch norm fusion.

Differential Revision: D79846881

Pull Request resolved: #2716

Author: abeakkas

torchao/quantization/pt2e/utils.py

@@ -758,7 +758,7 @@ def fold_bn_weights_into_conv_node(
     # since the node refers to a mutating op. Here we still need to call DCE first
     # to get rid of the unused getitem nodes that consume the BN node.
     m.graph.eliminate_dead_code()
-    if len(bn_node.users) == 0:
+    if not bn_node._erased and len(bn_node.users) == 0:
         m.graph.erase_node(bn_node)