dt-bindings: pwm: snps,dw-apb-timers: 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/68eaecf11db9bec7bdb90dbf38507332628a0434.1714450308.git.zhoubinbin@loongson.cnSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Documentation/devicetree/bindings/pwm/snps,dw-apb-timers-pwm2.yaml

@@ -51,7 +51,6 @@ properties:
 required:
   - compatible
   - reg
-  - "#pwm-cells"
   - clocks
   - clock-names