Minorly modify model_rd_for_sb_y function
Minorly modify model_rd_for_sb_y function

Added a skip_dc check. If skip_dc = 1, we could eliminate calling
of vp9_model_rd_from_var_lapndz(). This gave slight PSNR & SSIM
gain(<0.1%), and no speed change.

Change-Id: If5ca733366148c86b98e196a00cc890f50e9a3e5

Distrotech/libvpx,reimaginemedia/webm.libvpx,webmproject/libvpx,jmvalin/aom,smarter/aom,zofuthan/libvpx,Topopiccione/libvpx,abwiz0086/webm.libvpx,webmproject/libvpx,abwiz0086/webm.libvpx,lyx2014/libvpx_c,mwgoldsmith/vpx,running770/libvpx,felipebetancur/libvpx,matanbs/webm.libvpx,kalli123/webm.libvpx,Maria1099/webm.libvpx,Maria1099/webm.libvpx,jacklicn/webm.libvpx,ittiamvpx/libvpx-1,lyx2014/libvpx_c,GrokImageCompression/aom,openpeer/libvpx_new,mwgoldsmith/libvpx,shacklettbp/aom,kim42083/webm.libvpx,gshORTON/webm.libvpx,thdav/aom,kalli123/webm.libvpx,gshORTON/webm.libvpx,Maria1099/webm.libvpx,smarter/aom,kim42083/webm.libvpx,goodleixiao/vpx,mwgoldsmith/libvpx,webmproject/libvpx,reimaginemedia/webm.libvpx,shareefalis/libvpx,mwgoldsmith/libvpx,kalli123/webm.libvpx,Acidburn0zzz/webm.libvpx,ShiftMediaProject/libvpx,liqianggao/libvpx,thdav/aom,Acidburn0zzz/webm.libvpx,zofuthan/libvpx,running770/libvpx,goodleixiao/vpx,mbebenita/aom,thdav/aom,shyamalschandra/libvpx,Suvarna1488/webm.libvpx,VTCSecureLLC/libvpx,reimaginemedia/webm.libvpx,ittiamvpx/libvpx-1,shacklettbp/aom,VTCSecureLLC/libvpx,altogother/webm.libvpx,Acidburn0zzz/webm.libvpx,matanbs/webm.libvpx,shareefalis/libvpx,felipebetancur/libvpx,kalli123/webm.libvpx,thdav/aom,matanbs/webm.libvpx,gshORTON/webm.libvpx,stewnorriss/libvpx,Distrotech/libvpx,lyx2014/libvpx_c,mwgoldsmith/vpx,jmvalin/aom,iniwf/webm.libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,smarter/aom,Topopiccione/libvpx,altogother/webm.libvpx,shyamalschandra/libvpx,lyx2014/libvpx_c,GrokImageCompression/aom,mwgoldsmith/vpx,jacklicn/webm.libvpx,iniwf/webm.libvpx,luctrudeau/aom,iniwf/webm.libvpx,felipebetancur/libvpx,matanbs/webm.libvpx,mwgoldsmith/vpx,kalli123/webm.libvpx,jacklicn/webm.libvpx,thdav/aom,Suvarna1488/webm.libvpx,shyamalschandra/libvpx,lyx2014/libvpx_c,stewnorriss/libvpx,abwiz0086/webm.libvpx,running770/libvpx,abwiz0086/webm.libvpx,shacklettbp/aom,luctrudeau/aom,mwgoldsmith/libvpx,luctrudeau/aom,kim42083/webm.libvpx,Maria1099/webm.libvpx,kleopatra999/webm.libvpx,luctrudeau/aom,webmproject/libvpx,ShiftMediaProject/libvpx,GrokImageCompression/aom,ShiftMediaProject/libvpx,abwiz0086/webm.libvpx,jmvalin/aom,shyamalschandra/libvpx,Maria1099/webm.libvpx,VTCSecureLLC/libvpx,altogother/webm.libvpx,running770/libvpx,iniwf/webm.libvpx,GrokImageCompression/aom,smarter/aom,Acidburn0zzz/webm.libvpx,running770/libvpx,matanbs/webm.libvpx,iniwf/webm.libvpx,shyamalschandra/libvpx,ittiamvpx/libvpx-1,smarter/aom,zofuthan/libvpx,thdav/aom,reimaginemedia/webm.libvpx,Topopiccione/libvpx,goodleixiao/vpx,webmproject/libvpx,openpeer/libvpx_new,Distrotech/libvpx,stewnorriss/libvpx,running770/libvpx,reimaginemedia/webm.libvpx,zofuthan/libvpx,kim42083/webm.libvpx,abwiz0086/webm.libvpx,mbebenita/aom,Suvarna1488/webm.libvpx,lyx2014/libvpx_c,Acidburn0zzz/webm.libvpx,mbebenita/aom,altogother/webm.libvpx,jmvalin/aom,felipebetancur/libvpx,Acidburn0zzz/webm.libvpx,openpeer/libvpx_new,mbebenita/aom,shareefalis/libvpx,Distrotech/libvpx,jacklicn/webm.libvpx,kalli123/webm.libvpx,goodleixiao/vpx,kleopatra999/webm.libvpx,jacklicn/webm.libvpx,shareefalis/libvpx,Suvarna1488/webm.libvpx,kleopatra999/webm.libvpx,Suvarna1488/webm.libvpx,ShiftMediaProject/libvpx,felipebetancur/libvpx,openpeer/libvpx_new,ittiamvpx/libvpx-1,jacklicn/webm.libvpx,shyamalschandra/libvpx,VTCSecureLLC/libvpx,mwgoldsmith/libvpx,liqianggao/libvpx,mbebenita/aom,kleopatra999/webm.libvpx,liqianggao/libvpx,Distrotech/libvpx,shacklettbp/aom,VTCSecureLLC/libvpx,ittiamvpx/libvpx-1,mwgoldsmith/vpx,felipebetancur/libvpx,mbebenita/aom,webmproject/libvpx,iniwf/webm.libvpx,mbebenita/aom,zofuthan/libvpx,mbebenita/aom,matanbs/webm.libvpx,gshORTON/webm.libvpx,goodleixiao/vpx,shareefalis/libvpx,smarter/aom,GrokImageCompression/aom,stewnorriss/libvpx,stewnorriss/libvpx,openpeer/libvpx_new,jmvalin/aom,reimaginemedia/webm.libvpx,jmvalin/aom,Suvarna1488/webm.libvpx,Distrotech/libvpx,shacklettbp/aom,altogother/webm.libvpx,mwgoldsmith/libvpx,liqianggao/libvpx,liqianggao/libvpx,kleopatra999/webm.libvpx,Topopiccione/libvpx,Maria1099/webm.libvpx,zofuthan/libvpx,ittiamvpx/libvpx-1,kleopatra999/webm.libvpx,luctrudeau/aom,shacklettbp/aom,gshORTON/webm.libvpx,kim42083/webm.libvpx,gshORTON/webm.libvpx,openpeer/libvpx_new,stewnorriss/libvpx,goodleixiao/vpx,kim42083/webm.libvpx,shareefalis/libvpx,altogother/webm.libvpx,Topopiccione/libvpx,Topopiccione/libvpx,GrokImageCompression/aom,VTCSecureLLC/libvpx,liqianggao/libvpx,mbebenita/aom,luctrudeau/aom