speed-up SetResidualSSE2
speed-up SetResidualSSE2

(was unnecessarily complicated)

Before:
VP8SetResidualCoeffs: checksum = 1127918   elapsed = 475 ms.

Change-Id: Ia54bef86c45f9f474622ff16e594bf1da4f67ebd
After:
VP8SetResidualCoeffs: checksum = 1127918   elapsed = 404 ms.

ya7lelkom/libwebp,ttyangf/libwebp,imazen/libwebp,ya7lelkom/libwebp,PKRoma/libwebp,zofuthan/libwebp,redengineer/libwebp,ya7lelkom/libwebp,imazen/libwebp,yohunl/libwebp,zofuthan/libwebp,ttyangf/libwebp,Aexyn/libwebp,ya7lelkom/libwebp,yohunl/libwebp,PKRoma/libwebp,redengineer/libwebp,webmproject/libwebp,redengineer/libwebp,ya7lelkom/libwebp,webmproject/libwebp,rxl194/libwebp,yohunl/libwebp,ttyangf/libwebp,zofuthan/libwebp,Aexyn/libwebp,imazen/libwebp,redengineer/libwebp,rxl194/libwebp,yohunl/libwebp,PKRoma/libwebp,redengineer/libwebp,imazen/libwebp,Aexyn/libwebp,PKRoma/libwebp,webmproject/libwebp,Aexyn/libwebp,imazen/libwebp,ttyangf/libwebp,ttyangf/libwebp,yohunl/libwebp,PKRoma/libwebp,rxl194/libwebp,zofuthan/libwebp,zofuthan/libwebp,rxl194/libwebp,webmproject/libwebp,PKRoma/libwebp,rxl194/libwebp,Aexyn/libwebp,webmproject/libwebp