ASoC: dt-bindings: add mclk provider support to stm32 i2s

Add master clock provider support to STM32 I2S.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Link: https://lore.kernel.org/r/20210205104404.18786-2-olivier.moysan@foss.st.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/st,stm32-i2s.yaml

@@ -54,6 +54,10 @@ properties:
   resets:
     maxItems: 1
 
+  "#clock-cells":
+    description: Configure the I2S device as MCLK clock provider.
+    const: 0
+
 required:
   - compatible
   - "#sound-dai-cells"