dt-bindings: stm32: dfsdm: update audio properties

- Add missing compatible property in audio node.
- Remove obsolete "st,stm32-dfsdm-pdm" compatible.
- Remove useless comment in adc io-channels description.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201020155709.2621-2-olivier.moysan@st.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.yaml

@@ -199,8 +199,6 @@ patternProperties:
               description:
                 From common IIO binding. Used to pipe external sigma delta
                 modulator or internal ADC output to DFSDM channel.
-                This is not required for "st,stm32-dfsdm-pdm" compatibility as
-                PDM microphone is binded in Audio DT node.
 
           required:
             - io-channels
@@ -235,6 +233,10 @@ patternProperties:
               description: child node
 
               properties:
+                compatible:
+                  enum:
+                    - st,stm32h7-dfsdm-dai
+
                 "#sound-dai-cells":
                   const: 0
 
@@ -244,6 +246,7 @@ patternProperties:
                     modulator or internal ADC output to DFSDM channel.
 
               required:
+                - compatible
                 - "#sound-dai-cells"
                 - io-channels