vpx_memset16: drop unnecessary local
vpx_memset16: drop unnecessary local

+ add a cast

Change-Id: I2965e7867223aa25bf688c988629ac57b4971905

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