Fix aten_add. aten_sub to handle 2-operand versions (#38367)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/38367
Reviewed By: Krovatkin
Differential Revision: D21550736
Pulled By: protonu
fbshipit-source-id: 83491d35cc9168af2208c4f19c423d23e7de836d
