Fix batch size for vision_maskrcnn (#1656)
Summary:
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1656
Reviewed By: xuzhao9
Differential Revision: D45975772
Pulled By: ezyang
fbshipit-source-id: 0f374ecf44377d010de220012bed439e1f3dcbfb
