sad_sse2: fix sad4xN(_avg) on windows
sad_sse2: fix sad4xN(_avg) on windows

reduce the register count by 1 to avoid xmm6 and unnecessarily
penalizing the other users of the base macro

Change-Id: I59605c9a41a31c1b74f67ec06a40d1a7f92c4699

thdav/aom,ShiftMediaProject/libvpx,shacklettbp/aom,GrokImageCompression/aom,ittiamvpx/libvpx-1,luctrudeau/aom,mwgoldsmith/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,Topopiccione/libvpx,mbebenita/aom,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,thdav/aom,smarter/aom,GrokImageCompression/aom,mwgoldsmith/vpx,webmproject/libvpx,mwgoldsmith/libvpx,GrokImageCompression/aom,smarter/aom,thdav/aom,Topopiccione/libvpx,mwgoldsmith/vpx,jmvalin/aom,mbebenita/aom,shacklettbp/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,shacklettbp/aom,GrokImageCompression/aom,jmvalin/aom,mwgoldsmith/libvpx,openpeer/libvpx_new,luctrudeau/aom,thdav/aom,webmproject/libvpx,mbebenita/aom,openpeer/libvpx_new,openpeer/libvpx_new,smarter/aom,webmproject/libvpx,mbebenita/aom,jmvalin/aom,ittiamvpx/libvpx-1,smarter/aom,jmvalin/aom,mbebenita/aom,GrokImageCompression/aom,ShiftMediaProject/libvpx,openpeer/libvpx_new,mwgoldsmith/vpx,openpeer/libvpx_new,jmvalin/aom,luctrudeau/aom,mwgoldsmith/vpx,shacklettbp/aom,ShiftMediaProject/libvpx,GrokImageCompression/aom,mwgoldsmith/libvpx,mwgoldsmith/vpx,smarter/aom,thdav/aom,smarter/aom,mwgoldsmith/libvpx,mbebenita/aom,luctrudeau/aom,shacklettbp/aom,Topopiccione/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx,luctrudeau/aom,mwgoldsmith/vpx,thdav/aom,Topopiccione/libvpx,webmproject/libvpx,mbebenita/aom,webmproject/libvpx,openpeer/libvpx_new,jmvalin/aom,shacklettbp/aom,webmproject/libvpx,ittiamvpx/libvpx-1,ShiftMediaProject/libvpx