drm/gm204/disp: some magic that fixes bringup of uninitialised outputs

Probably missing something here, doesn't make a lot of sense to write
or+link data into a register whose offset is calculated by the same
or+link info..

This is the all I've witnessed the binary driver and vbios doing so
far, so it'll do.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>