drm/radeon/kms/atom: fix duallink on some early DCE3.2 cards

Certain revisions of the vbios on DCE3.2 cards have a bug
in the transmitter control table which prevents duallink from
being enabled properly on some cards.  The action switch statement
jumps to the wrong offset for the OUTPUT_ENABLE action.  The fix
is to use the ENABLE action rather than the OUTPUT_ENABLE action
on the affected cards.  In fixed version of the vbios, both
actions jump to the same offset, so the change should be safe.

Reported-and-tested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>