dt-bindings: pwm: renesas,tpu: 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>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/renesas,tpu-pwm.yaml

@@ -68,7 +68,6 @@ properties:
 required:
   - compatible
   - reg
-  - '#pwm-cells'
   - clocks
   - power-domains