Device name should be a string, not bytes (#40322)
Summary:
I.e. do not accept `bytes` as possible type of `device` argument in
`torch.cuda._get_device_index`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40322
Differential Revision: D22176885
Pulled By: malfet
fbshipit-source-id: 2f3a46174161f1cdcf6a6ad94a31e54b18ad6186
