MPS backend not working

[ikmckenz]

With the default code, using the MPS backend does not work at all and only produces images that appear to be white noise.

Interestingly, even removing all the cuda autocasting and cudnn usage, as in this fork, does not work - it still only produces random snow.

Tested on an M1 Pro chip. Tested on both Monterey and Ventura, and with Pytorch stable 1.13.1 and the new Pytorch stable 2.0 that came out yesterday.