[fx] fix subgraph API call_module warning about no owning module (#61463)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61463
seems like a small oversight(?), current test fails when warnings are recorded. discovered this when calling `graph.call_module(existing_call_module_node.target)` and it raised a warning
Test Plan: `buck test //caffe2/test:fx`
Reviewed By: ansley
Differential Revision: D29637799
fbshipit-source-id: 2305629863230235f76a926fe2e4de480cbf853c
