drm/omap: Don't pass display pointer to encoder init function

drm/omap: Don't pass display pointer to encoder init function

The display isn't used by the encoder implementation, don't pass it to
the initialization function and store it internally needlessly.

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