dt-bindings: pwm: samsung: 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>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -86,7 +86,6 @@ required:
   - clocks
   - clock-names
   - compatible
-  - "#pwm-cells"
   - reg
 
 additionalProperties: false