mpc85xx: fix KEY_RFKILL vs KEY_RFKill

This fixes a buildbot builder error:
Error: arch/powerpc/boot/dts/tl-wdr4900-v1.dts:245.18-19 syntax error

Fixes: 256e1dbc ("mpc85xx: utilize dt-binding definitions for keys + gpios")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/mpc85xx/files/arch/powerpc/boot/dts/tl-wdr4900-v1.dts

@@ -242,7 +242,7 @@
 		rfkill {
 			label = "RFKILL switch";
 			gpios = <&gpio0 11 GPIO_ACTIVE_LOW>;
-			linux,code = <KEY_RFKill>;
+			linux,code = <KEY_RFKILL>;
 		};
 	};
 };