vp8-denoiser: Fix threshold for skin map.
vp8-denoiser: Fix threshold for skin map.

Make it consistent with the comment/intended behavior,
that is, only denoise if current block is zero_mv.

Change-Id: I3909761e802e80089752a493ab3646dc32698ded

ittiamvpx/libvpx-1,Topopiccione/libvpx,webmproject/libvpx,webmproject/libvpx,Topopiccione/libvpx,luctrudeau/aom,ittiamvpx/libvpx-1,webmproject/libvpx,luctrudeau/aom,mwgoldsmith/vpx,mbebenita/aom,mwgoldsmith/vpx,mwgoldsmith/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,luctrudeau/aom,mwgoldsmith/libvpx,smarter/aom,webmproject/libvpx,Topopiccione/libvpx,mbebenita/aom,ittiamvpx/libvpx-1,Topopiccione/libvpx,luctrudeau/aom,GrokImageCompression/aom,mwgoldsmith/vpx,smarter/aom,smarter/aom,mbebenita/aom,ShiftMediaProject/libvpx,GrokImageCompression/aom,GrokImageCompression/aom,mwgoldsmith/vpx,mbebenita/aom,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,smarter/aom,webmproject/libvpx,mbebenita/aom,smarter/aom,ShiftMediaProject/libvpx,Topopiccione/libvpx,smarter/aom,luctrudeau/aom,ittiamvpx/libvpx-1,mwgoldsmith/libvpx,mbebenita/aom,mbebenita/aom,ittiamvpx/libvpx-1,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,ittiamvpx/libvpx-1,webmproject/libvpx,luctrudeau/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,Topopiccione/libvpx,ShiftMediaProject/libvpx