fix pca_lowrank memory consumption (#40853)
Summary:
Per title, fixes https://github.com/pytorch/pytorch/issues/40768
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40853
Reviewed By: pbelevich
Differential Revision: D22363906
Pulled By: ngimel
fbshipit-source-id: 966a4b230d351f7632c5cfae4a3b7c9a787bc9a5
