ASoC: dt-bindings: rt5682: Add #sound-dai-cells

The rt5682 codec can be pointed to through a sound-dai property to be
used as part of a machine sound driver. dtc expects #sound-dai-cells to
be defined in the codec's node in those cases, so add it in the
dt-binding and set it to 0.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20220429203039.2207848-4-nfraprado@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>