ASoC: dt-bindings: Use OF graph schema

Now that we have an OF graph schema, let's use it for the
audio-graph-port schema.

Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: alsa-devel@alsa-project.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210331142748.2163272-3-robh@kernel.org


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