backlight pwm period changed to 40000us to fix high pitch noise issue at 10Khz

Author: Vincent-FK

arch/arm/boot/dts/sun8i-v3s-funkey.dts

@@ -58,7 +58,7 @@
 
 	backlight: backlight {
 		compatible = "pwm-backlight";
-		pwms = <&pwm 0 100000 1>;
+		pwms = <&pwm 0 40000 1>;
 		brightness-levels = <0 1 2 3 8 14 21 32 46 60 80 100>; //2.2 div factor
 		default-brightness-level = <11>;
 		power-supply = <&reg_vcc5v0>;