Fixes the pink line that shows up with some hdmi monitors.  This
will need to be revisited when audio support is added.

Fixes:
http://bugs.freedesktop.org/show_bug.cgi?id=27452Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>