ASoC: dt-bindings: rockchip,rk3308-codec: add port property

Fix DTB warnings when rk3308-codec used with audio-graph-card by
documenting port property:

codec@ff560000: 'port' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Dmitry Yashin <dmt.yashin@gmail.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://patch.msgid.link/20241028213314.476776-2-dmt.yashin@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>