ARM: dts: exynos: Add missing unit name to memory nodes in Exynos3 DTS

This patch fixes the following DTC warnings:

"Node /memory has a reg or ranges property, but no unit name"
Signed-off-by: NJavier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>

arch/arm/boot/dts/exynos3250-artik5.dtsi

@@ -24,7 +24,7 @@
 		stdout-path = &serial_2;
 	};
 
-	memory {
+	memory@40000000 {
 		device_type = "memory";
 		reg = <0x40000000 0x1ff00000>;
 	};

arch/arm/boot/dts/exynos3250-monk.dts

@@ -27,7 +27,7 @@
 		i2c7 = &i2c_max77836;
 	};
 
-	memory {
+	memory@40000000 {
 		device_type = "memory";
 		reg =  <0x40000000 0x1ff00000>;
 	};

arch/arm/boot/dts/exynos3250-rinato.dts

@@ -27,7 +27,7 @@
 		i2c7 = &i2c_max77836;
 	};
 
-	memory {
+	memory@40000000 {
 		device_type = "memory";
 		reg =  <0x40000000 0x1ff00000>;
 	};