[quant] Fix docs error in convert_fx (#67152)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/67152
Test Plan:
```
cd docs
make html
```
Imported from OSS
Reviewed By: supriyar
Differential Revision: D31884570
fbshipit-source-id: 2b521f617c93f6fa08da3387df2d25497293eee6
