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

Documentation/devicetree/bindings/sound/rt5682.txt

@@ -46,6 +46,8 @@ Optional properties:
 
 - realtek,dmic-clk-driving-high : Set the high driving of the DMIC clock out.
 
+- #sound-dai-cells: Should be set to '<0>'.
+
 Pins on the device (for linking into audio routes) for RT5682:
 
   * DMIC L1