ARM: dts: imx6ul-geam: 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-geam.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>

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

@@ -21,7 +21,7 @@ memory@80000000 {
 
 	backlight {
 		compatible = "pwm-backlight";
-		pwms = <&pwm8 0 100000>;
+		pwms = <&pwm8 0 100000 0>;
 		brightness-levels = < 0  1  2  3  4  5  6  7  8  9
 				     10 11 12 13 14 15 16 17 18 19
 				     20 21 22 23 24 25 26 27 28 29
@@ -194,7 +194,6 @@ timing0: timing0 {
 };
 
 &pwm8 {
-	#pwm-cells = <2>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_pwm8>;
 	status = "okay";