Specify to use Float16UniformFill if necessary in sparse lookup layer (#18499)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18499
If the init op is not fp16 compatible, it should throw.
However, in the special case where the original init op is UniformFill,
we replace it with Float16UniformFill
Reviewed By: kennyhorror
Differential Revision: D14627209
fbshipit-source-id: eb427772874a732ca8b3a25d06670d119ce8ac14
