r600g: fix the CB_SHADER_MASK setup
This fixes the single-sample fast clear hang. Cc: 10.6 <mesa-stable@lists.freedesktop.org> Tested-by:Dieter Nützel <Dieter@nuetzel-hh.de> Reviewed-by:
Dave Airlie <airlied@redhat.com> (cherry picked from commit d4ad4c20)