drm/omap: Remove supported output check in CRTC connect handler

The CRTC connect handler checks whether the DSS output supports the
DISPC channel assigned to it. As the channel is assigned to the output
by the output driver a failure there could only result from a driver
bug. All the output drivers have been verified and they are always
assigned a DISPC channel that is supported on the SoC they run on. The
check can thus be removed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>