drm/tidss: Remove return values from dispc_plane_{setup, enable}()

Calls to dispc_plane_setup() and dispc_plane_enable() cannot fail.
Remove the return value.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209154107.30680-6-tzimmermann@suse.de