dt-bindings: pwm: marvell,pxa: Do not require pwm-cells twice

pwm-cells property is already required by pwm.yaml schema.
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/06765e0dd9a842dc51ff9c9cea93f26b8792e44b.1714450308.git.zhoubinbin@loongson.cnSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Documentation/devicetree/bindings/pwm/marvell,pxa-pwm.yaml

@@ -34,7 +34,6 @@ properties:
 required:
   - compatible
   - reg
-  - "#pwm-cells"
   - clocks
 
 additionalProperties: false