In interpolate, use if instead of elif (#37171)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37171
Every one of these branches returns or raises, so there's no need for elif.
This makes it a little easier to reorder and move conditions.
ghstack-source-id: 106938110
Test Plan: Existing test for interpolate.
Differential Revision: D21209992
fbshipit-source-id: 5c517e61ced91464b713f7ccf53349b05e27461c
