Fix exir deserialization logic (#2857)

Summary:

Looks like a recent str -> TensorArgument change in diff D54855251 wasn't very thorough. ETRecord deserialization failed because of it.

Differential Revision: D55776877

Author: Olivia-liu

exir/serde/export_serialize.py

@@ -1503,7 +1503,7 @@ def deserialize_optional_tensor_args(a):
                     if a.type == "as_none":
                         return None
                     elif a.type == "as_tensor":
-                        return self.serialized_name_to_node[a.value]
+                        return self.serialized_name_to_node[a.value.name]
                     else:
                         raise SerializeError(f"Unhandled argument {inp}")