Pass loop_over optional parameter for cached reader properly. (#21929)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21929
Just need to pass `loop_over` argument properly.
Reviewed By: noname01
Differential Revision: D15885401
fbshipit-source-id: f1928277262a80e5b41f4c4f3945c2f378a4e233
