floating point precision will cause rgb*max generate different value on x86_32 and x86_64. have pass fate test on x86_32 and x86_64 by using lrintf to get the nearest integral value for rgb * max before av_clip. Reviewed-by: Paul B Mahol <onemda@gmail.com> Signed-off-by: Limin Wang <lance.lmwang@gmail.com>