Fix the shape of PReLU weight (#21330)
Summary:
Fix issue https://github.com/pytorch/pytorch/issues/21271
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21330
Reviewed By: zrphercule
Differential Revision: D15776459
Pulled By: houseroad
fbshipit-source-id: 4e0aef88e9c91c79faa3da6fa66f7466dee52018
