ARM: dts: imx51-babbage: Use predefined constants for keys definition

Signed-off-by: NAlexander Shiyan <shc_work@mail.ru>
Signed-off-by: NShawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/imx51-babbage.dts

@@ -88,7 +88,7 @@
 		power {
 			label = "Power Button";
 			gpios = <&gpio2 21 GPIO_ACTIVE_HIGH>;
-			linux,code = <116>; /* KEY_POWER */
+			linux,code = <KEY_POWER>;
 			gpio-key,wakeup;
 		};
 	};