Fixed seek offset size to 64bit. (#27047)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/26998
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27047
Differential Revision: D17666050
Pulled By: ezyang
fbshipit-source-id: f02ebd5320ae25f8949be20d0744fe3cd3e2fee9
