fix bug when perform classification in resnet
fix bug when perform classification in resnet

Summary: Pull Request resolved: https://github.com/facebookresearch/detectron2/pull/759

Differential Revision: D19599357

Pulled By: ppwwyyxx

fbshipit-source-id: 8608d418d872f75c0ff99dece7152a180e685571

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2