Drop extra Reshape in attention calculation
Drop extra Reshape in attention calculation

Summary: We can avoid this extra Reshape.

Reviewed By: jamesr66a

Differential Revision: D5032874

fbshipit-source-id: 92bd568bc6bec53d7f81a64cfa96d2c610823f8c

bwasti/caffe2,davinwang/caffe2,sf-wind/caffe2,bwasti/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,pietern/caffe2,bwasti/caffe2,sf-wind/caffe2,sf-wind/caffe2,davinwang/caffe2,caffe2/caffe2,Yangqing/caffe2,pietern/caffe2,bwasti/caffe2,sf-wind/caffe2,davinwang/caffe2,xzturn/caffe2,sf-wind/caffe2,xzturn/caffe2,Yangqing/caffe2,pietern/caffe2,bwasti/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2