Fixed seek offset size to 64bit. (#27125)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/26998.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27125
Differential Revision: D17687154
Pulled By: ezyang
fbshipit-source-id: 6784f4fd799130ac72a25884f120a0ba96bd4f51
