ARM: dts: imx6q-pistachio: 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/imx6q-pistachio.dtb: pwm@2080000: #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/imx6q-pistachio.dts

@@ -124,7 +124,7 @@ sound {
 
 	backlight_lvds: backlight-lvds {
 		compatible = "pwm-backlight";
-		pwms = <&pwm1 0 50000>;
+		pwms = <&pwm1 0 50000 0>;
 		brightness-levels = <
 			0  /*1  2  3  4  5  6*/  7  8  9
 			10 11 12 13 14 15 16 17 18 19
@@ -571,7 +571,6 @@ lvds0_out: endpoint {
 };
 
 &pwm1 {
-	#pwm-cells = <2>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_pwm1>;
 	status = "okay";