Replace duplicative s with alpha (#56804)
Summary:
It is always easier to read a document when different objects / concepts denoted with different variables / representations.
In this PR we make sure the [complex autograd](https://pytorch.org/docs/master/notes/autograd.html#autograd-for-complex-numbers) documentation, the variable of output and step size diverge.
Fixes https://github.com/pytorch/pytorch/issues/53633
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56804
Reviewed By: anjali411
Differential Revision: D27989959
Pulled By: iramazanli
fbshipit-source-id: c271590ee744c8aeeff62bfaa2295429765ef64e
