ARM64: dts: marvell: Fixup memory DT warning for Armada 37xx

memory has a reg property so the unit name should contain an address.
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

arch/arm64/boot/dts/marvell/armada-3720-db.dts

@@ -56,7 +56,7 @@ chosen {
 		stdout-path = "serial0:115200n8";
 	};
 
-	memory {
+	memory@0 {
 		device_type = "memory";
 		reg = <0x00000000 0x00000000 0x00000000 0x20000000>;
 	};

arch/arm64/boot/dts/marvell/armada-3720-espressobin.dts

@@ -55,7 +55,7 @@ chosen {
 		stdout-path = "serial0:115200n8";
 	};
 
-	memory {
+	memory@0 {
 		device_type = "memory";
 		reg = <0x00000000 0x00000000 0x00000000 0x20000000>;
 	};