fixing the lamest bug in swscale, all the rgb/bgr->* code did 2x2 downsampling...

fixing the lamest bug in swscale, all the rgb/bgr->* code did 2x2 downsampling for chroma, it should just be 2x1 (the rest of the code also belived its 2x1 ...)


git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@20961 b3059339-0415-0410-9bf9-f77b7e298cf2