ARM: dts: imx53-smd: Do not hardcode input codes

Instead of hardcoding the input codes we can use the symbol name for
better readability.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx53-smd.dts

@@ -11,6 +11,7 @@
  */
 
 /dts-v1/;
+#include <dt-bindings/input/input.h>
 #include "imx53.dtsi"
 
 / {
@@ -27,13 +28,13 @@
 		volume-up {
 			label = "Volume Up";
 			gpios = <&gpio2 14 0>;
-			linux,code = <115>; /* KEY_VOLUMEUP */
+			linux,code = <KEY_VOLUMEUP>;
 		};
 
 		volume-down {
 			label = "Volume Down";
 			gpios = <&gpio2 15 0>;
-			linux,code = <114>; /* KEY_VOLUMEDOWN */
+			linux,code = <KEY_VOLUMEDOWN>;
 		};
 	};
 };