dt-bindings: sound: rockchip-i2s: add #sound-dai-cells property

'#sound-dai-cells' is required to properly interpret
the list of DAI specified in the 'sound-dai' property,
so add them to 'rockchip-i2s.yaml'

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200324094149.6904-2-jbx6244@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip-i2s.yaml

@@ -77,6 +77,9 @@ properties:
       Required property for controllers which support multi channel
       playback/capture.
 
+  "#sound-dai-cells":
+    const: 0
+
 required:
   - compatible
   - reg
@@ -85,6 +88,7 @@ required:
   - clock-names
   - dmas
   - dma-names
+  - "#sound-dai-cells"
 
 additionalProperties: false
 
@@ -103,4 +107,5 @@ examples:
       dma-names = "tx", "rx";
       rockchip,capture-channels = <2>;
       rockchip,playback-channels = <8>;
+      #sound-dai-cells = <0>;
     };