ar71xx: flag FritzBox 4020 buttons as active low

Buttons of AVM FritzBox 4020 are incorrectly flagged as active high.

This was an oversight as RFKill button was working as expected even
with incorrectly flagged GPIO.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ar71xx/files/arch/mips/ath79/mach-fritz4020.c

@@ -169,7 +169,7 @@ static struct gpio_keys_button fritz4020_gpio_keys[] __initdata = {
 		.code			= KEY_RFKILL,
 		.debounce_interval	= FRITZ4020_KEYS_DEBOUNCE_INTERVAL,
 		.gpio			= FRITZ4020_GPIO_BTN_WLAN,
-		.active_low		= 0,
+		.active_low		= 1,
 	},
 	{
 		.desc			= "WPS button",
@@ -177,7 +177,7 @@ static struct gpio_keys_button fritz4020_gpio_keys[] __initdata = {
 		.code			= KEY_WPS_BUTTON,
 		.debounce_interval	= FRITZ4020_KEYS_DEBOUNCE_INTERVAL,
 		.gpio			= FRITZ4020_GPIO_BTN_WPS,
-		.active_low		= 0,
+		.active_low		= 1,
 	},
 };