HFTracer.trace should use/return self.graph to be compatible with tor…

…ch.fx.Tracer (huggingface#15824)

src/transformers/utils/fx.py

@@ -472,7 +472,7 @@ def trace(
 
         self._patch_leaf_functions_for_root(root)
 
-        graph = super().trace(root, concrete_args=concrete_args)
+        self.graph = super().trace(root, concrete_args=concrete_args)
 
         self._patch_leaf_functions_for_root(root, restore=True)
 
@@ -482,16 +482,16 @@ def trace(
         # This is necessary because concrete args are added as input to the traced module since
         # https://github.com/pytorch/pytorch/pull/55888.
         # A PR that solves this was posted: https://github.com/pytorch/pytorch/pull/59569 but it was not merged yet.
-        for node in graph.nodes:
+        for node in self.graph.nodes:
             if node.op == "placeholder":
                 # Removing default values for inputs as the forward pass will fail with them.
                 if node.target in input_names:
                     node.args = ()
                 # It is a concrete arg so it is not used and should be removed.
                 else:
-                    graph.erase_node(node)
+                    self.graph.erase_node(node)
 
-        return graph
+        return self.graph
 
     def _insert_module_as_submodule(self, mod: nn.Module) -> str:
         """