drm/bridge: tc358767: use bridge mode_valid

We have tc_connector_mode_valid() to filter out videomdoes that the
tc358767 cannot support. As it is a bridge limitation, change the code
to use drm_bridge_funcs's mode_valid instead.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-19-tomi.valkeinen@ti.com