Fix docs so that the example works (#30120)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30120
The example given for functional conv2d didn't work. This diff fixes the example in docs so that it works.
Fixes https://github.com/pytorch/pytorch/issues/29649
ghstack-source-id: 94601559
Test Plan: Tried the example locally
Differential Revision: D18604606
fbshipit-source-id: ff1a4f903e2843efe30d962d4ff00e5065cd1d7e
