drm/omap: dss: Remove duplicated parameter to dss_mgr_(dis)connect()

The dss_mgr_connect() and dss_mgr_disconnect() functions take two
omap_dss_device pointers as parameters, which are always set to the same
value by all callers. Remove the duplicated pointer.

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>