ARM: dts: bcm28155-ap: Fix Card Detection GPIO

The board schematic states that the "SD_CARD_DET_N gets pulled to GND
when card is inserted" so the polarity has been updated to active low.

Polarity is now specified with a GPIO define instead of a magic number.
Signed-off-by: NTim Kryger <tim.kryger@linaro.org>
Reviewed-by: NMatt Porter <matt.porter@linaro.org>
Signed-off-by: NOlof Johansson <olof@lixom.net>

arch/arm/boot/dts/bcm28155-ap.dts

@@ -13,6 +13,8 @@
 
 /dts-v1/;
 
+#include <dt-bindings/gpio/gpio.h>
+
 #include "bcm11351.dtsi"
 
 / {
@@ -60,7 +62,7 @@
 
 	sdio4: sdio@3f1b0000 {
 		max-frequency = <48000000>;
-		cd-gpios = <&gpio 14 0>;
+		cd-gpios = <&gpio 14 GPIO_ACTIVE_LOW>;
 		status = "okay";
 	};