ARM: dts: fix pwm-cells in pwm node for exynos4

pwm-cells should be 3. Third cell is optional PWM flags. And This flag
supported by this binding is PWM_POLARITY_INVERTED.
Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Reviewed-by: Sachin Kamat <sachin.kamat@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/boot/dts/exynos4.dtsi

@@ -554,7 +554,7 @@ pwm@139D0000 {
 		interrupts = <0 37 0>, <0 38 0>, <0 39 0>, <0 40 0>, <0 41 0>;
 		clocks = <&clock CLK_PWM>;
 		clock-names = "timers";
-		#pwm-cells = <2>;
+		#pwm-cells = <3>;
 		status = "disabled";
 	};