drm: rcar-du: lvds: Call function directly instead of through pointer

When disabling the companion bridge in rcar_lvds_atomic_disable(),
there's no need to go through the bridge's operations to call
.atomic_disable(). Call rcar_lvds_atomic_disable() on the companion
directly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>