drm/nouveau: Workaround incorrect DCB entry on a GeForce3 Ti 200.

Fixes the DVI-D output on that board (fdo bug 32645).

Reported-by: Bryan Quigley <BryanQuigley@Ubuntu.com>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>