Stop using :attr: in functorch docs (#91015)
We're using :attr: wrong. :attr: refers to an attribute of a Python
object, not the parameter to a function:
- https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html#role-py-attr
This leads to some weird things when moving to torch.func: sphinx
decides to link torch.func for :attr:`func`
Test Plan:
- docs preview.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91015
Approved by: https://github.com/samdow
