fix densepose dataloader path
fix densepose dataloader path

Summary: Pull Request resolved: https://github.com/facebookresearch/detectron2/pull/287

Differential Revision: D18418943

Pulled By: ppwwyyxx

fbshipit-source-id: ca3117e8461fda9e69fe251ce7c6f13365fe84cd

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2