The binding dictates using 3 pwm-cells. Adhere to that.
This fixes the following dtbs_check warnings:
	arch/arm/boot/dts/nxp/imx/imx6ul-kontron-bl.dtb: pwm@
20fc000: #pwm-cells:0:0: 3 was expected
		from schema : http://devicetree.org/schemas/pwm/imx-pwm.yaml#
	arch/arm/boot/dts/nxp/imx/imx6ul-kontron-bl-43.dtb: pwm@
20fc000: #pwm-cells:0:0: 3 was expected
		from schema : http://devicetree.org/schemas/pwm/imx-pwm.yaml#
	arch/arm/boot/dts/nxp/imx/imx6ull-kontron-bl.dtb: pwm@
20fc000: #pwm-cells:0:0: 3 was expected
		from schema : http://devicetree.org/schemas/pwm/imx-pwm.yaml#
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
 
        pwm-beeper {
                compatible = "pwm-beeper";
-               pwms = <&pwm8 0 5000>;
+               pwms = <&pwm8 0 5000 0>;
        };
 
        reg_3v3: regulator-3v3 {
 };
 
 &pwm8 {
-       #pwm-cells = <2>;
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_pwm8>;
        status = "okay";