ARM: dts: imx6ul-phytec-phycore-som: Add missing unit name

Pass the memory unit name in order to fix the following build warning
with W=1:

arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi:23.9-26.4: Warning (unit_address_vs_reg): /memory: node has a reg or ranges property, but no unit name

Cc: Stefan Riedmueller <[e-mail]>
Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi

···
 	 * Set the minimum memory size here and
 	 * let the bootloader set the real size.
 	 */
-	memory {
+	memory@80000000 {
 		device_type = "memory";
 		reg = <0x80000000 0x8000000>;
 	};