ARM: dts: imx6ul-ccimx6ulsbcpro: Use #pwm-cells = <3> for imx27-pwm device

The binding dictates using 3 pwm-cells. Adhere to that.

This fixes the following dtbs_check warning:

	arch/arm/boot/dts/nxp/imx/imx6ul-ccimx6ulsbcpro.dtb: pwm@20f0000: #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>

arch/arm/boot/dts/nxp/imx/imx6ul-ccimx6ulsbcpro.dts

@@ -18,7 +18,7 @@ / {
 
 	lcd_backlight: backlight {
 		compatible = "pwm-backlight";
-		pwms = <&pwm5 0 50000>;
+		pwms = <&pwm5 0 50000 0>;
 		brightness-levels = <0 4 8 16 32 64 128 255>;
 		default-brightness-level = <6>;
 		status = "okay";
@@ -168,7 +168,6 @@ &pwm4 {
 };
 
 &pwm5 {
-	#pwm-cells = <2>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_pwm5>;
 	status = "okay";