drm/sti: fixup for bridge interface

So sti doesn't build because the bridge interfaces changes didn't
catch up to its new DVO driver.

Now I might just carry this patch, but I might just push the
bridge pull into a side-pull until someone resolves it.

So this might not be the right solution to the problem, so
please figure it out and let me know ASAP.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>