fix dangling ptr in embedding_bag (#44571)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/44571
Test Plan: Imported from OSS
Reviewed By: malfet, ngimel
Differential Revision: D23661007
Pulled By: glaringlee
fbshipit-source-id: e4a54acd0de55f275828c1d1289a1f069de07291
