dt-bindings: pwm: brcm,bcm7038: Do not require pwm-cells twice

pwm-cells property is already required by pwm.yaml schema.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/brcm,bcm7038-pwm.yaml

@@ -28,7 +28,6 @@ properties:
 required:
   - compatible
   - reg
-  - "#pwm-cells"
   - clocks
 
 additionalProperties: false