drm/radeon/kms: fix washed out image on legacy tv dac

bad cast was overwriting the tvdac adj values
Fixes fdo bug 27478

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
1 file changed