[MPS] Fix batch_norm_backwards key (#98794) (#99456)
One needs different graphs for batch_norm_backwards depending whether or
not gradients are required for some of the params
Fixes https://github.com/pytorch/pytorch/issues/98602
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98794
Approved by: https://github.com/kulinseth
(cherry picked from commit 583193e1d90e795d1b4bb607368a18bc9ae3f09c)
