dt-bindings:iio:adc:adi,ad7124: Use the new adc.yaml channel binding

This both ensures this binding is compliant with the generic properties
and reduces the amount we need to specify in this separate binding.

Whilst here mark the child node as additionalProperties: false
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Michael Hennerich <Michael.Hennerich@analog.com>
Link: https://lore.kernel.org/r/20201031182423.742798-3-jic23@kernel.org

Documentation/devicetree/bindings/iio/adc/adi,ad7124.yaml

@@ -63,10 +63,10 @@ required:
 
 patternProperties:
   "^channel@([0-9]|1[0-5])$":
+    $ref: "adc.yaml"
     type: object
     description: |
       Represents the external channels which are connected to the ADC.
-      See Documentation/devicetree/bindings/iio/adc/adc.txt.
 
     properties:
       reg:
@@ -88,15 +88,9 @@ patternProperties:
         $ref: /schemas/types.yaml#/definitions/uint32
         enum: [0, 1, 3]
 
-      diff-channels:
-        description: see Documentation/devicetree/bindings/iio/adc/adc.txt
-        items:
-          minimum: 0
-          maximum: 15
+      diff-channels: true
 
-      bipolar:
-        description: see Documentation/devicetree/bindings/iio/adc/adc.txt
-        type: boolean
+      bipolar: true
 
       adi,buffered-positive:
         description: Enable buffered mode for positive input.
@@ -110,6 +104,8 @@ patternProperties:
       - reg
       - diff-channels
 
+    additionalProperties: false
+
 additionalProperties: false
 
 examples: