fixes indices computation for trilinear interpolate backwards (#50084)
Summary:
https://github.com/pytorch/pytorch/issues/48675 had some typos in indices computations so that results for trilinear interpolation where height is not equal to width were wrong. This PR fixes it.
cc xwang233
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50084
Reviewed By: BIT-silence
Differential Revision: D25777083
Pulled By: ngimel
fbshipit-source-id: 71be545628735fe875b7ea30bf6a09df4f2fae5c
