dt-bindings: pwm: iqs620a: Include generic PWM schema

Include generic pwm.yaml schema, which enforces PWM node naming and
brings pwm-cells requirement.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Jeff LaBundy <jeff@labundy.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/iqs620a-pwm.yaml

@@ -15,6 +15,9 @@ description: |
   Documentation/devicetree/bindings/mfd/iqs62x.yaml for further details as
   well as an example.
 
+allOf:
+  - $ref: pwm.yaml#
+
 properties:
   compatible:
     enum:
@@ -25,7 +28,6 @@ properties:
 
 required:
   - compatible
-  - "#pwm-cells"
 
 additionalProperties: false