fix soft_nms_cpu call in BoxWithNMSLimit (#20738)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20738
D15348610 introduces a bug of misaligned arguments.
Reviewed By: isameer
Differential Revision: D15425627
fbshipit-source-id: b6345863847426ae04eb31245d13f7fcb69d0355
