dt-bindings: iio: ad7192: Fix Regulator Properties

The AD7192 binding describes two regulator properties, avdd-supply and
dvdd-supply, but describes it as a constant string that must be avdd and
dvdd. This is wrong since a *-supply property is actually a phandle, and
results in warnings when the example is validated (or any device tree using
that device, for that matter).

Let's remove that requirement.

Fixes: f7356e4703 ("dt-bindings: iio: adc: ad7192: Add binding documentation for AD7192")
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/iio/adc/adi,ad7192.yaml

@@ -43,13 +43,9 @@ properties:
 
   dvdd-supply:
     description: DVdd voltage supply
-    items:
-      - const: dvdd
 
   avdd-supply:
     description: AVdd voltage supply
-    items:
-      - const: avdd
 
   adi,rejection-60-Hz-enable:
     description: |