Use at::cpu in bench_approx (#56563)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/56563
Test Plan: Imported from OSS
Reviewed By: navahgar
Differential Revision: D27902737
Pulled By: bertmaher
fbshipit-source-id: 66962671afbb093d5ae0b9308a401536c06ce8f5
