Fix function signature in ATenOp for at::Half Set function (GPU version)
Fix function signature in ATenOp for at::Half Set function (GPU version)

Summary:
The CPU version is fixed here. https://github.com/caffe2/caffe2/pull/1464/files

Now fix GPU version.
Closes https://github.com/caffe2/caffe2/pull/1506

Reviewed By: jamesr66a

Differential Revision: D6392830

Pulled By: houseroad

fbshipit-source-id: 922205630cbd8e24da80e269c6cd32bc4f040100

davinwang/caffe2,xzturn/caffe2,davinwang/caffe2,Yangqing/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,caffe2/caffe2,Yangqing/caffe2,xzturn/caffe2,davinwang/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,davinwang/caffe2,xzturn/caffe2