Fix IDE hint channels_last & preserve_format (#39120)
Summary:
- Fixing the nit introduced in https://github.com/pytorch/pytorch/issues/38784 .
- [torch.preserve_format] does not show IDE hint either, it would be fixed here as well.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39120
Differential Revision: D21904575
Pulled By: ezyang
fbshipit-source-id: 80fa1e838e0c444d7b1f2d45e649b51d6c38b54d
