arm: zynq: Add missing address node name in microzed board

This patch is fixing issue reported by dtc:
arch/arm/boot/dts/zynq-microzed.dtb: Warning (unit_address_vs_reg): Node
/memory has a reg or ranges property, but no unit name

Signed-off-by: Michal Simek <michal.simek@xilinx.com>