drm/omap: fix panel/encoder probes

The recent changes which removed platform data support from panels &
encoders had a few mistakes, causing probes of DVI connector and DSI
command mode panels to fail every time due to missing '!'. Fix the
if()s.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>