ASoC: dt-bindings: audio-graph-port: add missing mclk-fs

audio-graph-port is missing "mclk-fs" on ports/port,
it is used not only endpoint. It is already defined on simple-card.
This patch fixup it.
Without this patch, we will get below warning.

${LINUX}/arch/arm64/boot/dts/renesas/r8a77951-ulcb-kf.dtb: audio-codec@44: ports: 'mclk-fs' does not match any of the regexes: '^port@[0-9a-f]+$', 'pinctrl-[0-9]+'
	From schema: ${LINUX}/Documentation/devicetree/bindings/sound/ti,pcm3168a.yaml

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87o7qp7rgp.wl-kuninori.morimoto.gx@renesas.com


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