Update _torch_docs / ldexp (#86721)
Fixes a typo on ldexp docstring.
https://pytorch.org/docs/master/generated/torch.ldexp.html?highlight=ldexp#torch.ldexp
<img width="976" alt="image" src="https://user-images.githubusercontent.com/2459423/195191117-15b4e1f3-dfd5-466c-b5aa-72851f0c2393.png">
https://livesphinx.herokuapp.com/
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86721
Approved by: https://github.com/samdow
