dt-bindings:iio:adc:adi,ad7768-1: Add documentation for channel label

Optional attribute for better identification of the channels.
Signed-off-by: Cristian Pop <cristian.pop@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200928090959.88842-4-cristian.pop@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7768-1.yaml

@@ -29,6 +29,12 @@ properties:
   interrupts:
     maxItems: 1
 
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 0
+
   vref-supply:
     description:
       ADC reference voltage supply
@@ -61,6 +67,24 @@ required:
   - spi-cpha
   - adi,sync-in-gpios
 
+patternProperties:
+  "^channel@([0-9]|1[0-5])$":
+    type: object
+    description: |
+      Represents the external channels which are connected to the device.
+
+    properties:
+      reg:
+        description: |
+          The channel number.
+
+      label:
+        description: |
+          Unique name to identify which channel this is.
+    required:
+      - reg
+    additionalProperties: false
+
 additionalProperties: false
 
 examples:
@@ -84,6 +108,14 @@ examples:
             reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
             clocks = <&ad7768_mclk>;
             clock-names = "mclk";
+
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            channel@0 {
+                reg = <0>;
+                label = "channel_0";
+            };
         };
     };
 ...