arm: mvebu: armada-388-gp.dts: Fix dtc warnings

Fix these dtc warnings:
Warning (reg_format)
Warning (avoid_default_addr_size)
Signed-off-by: NStefan Roese <sr@denx.de>
Cc: Chris Packham <judge.packham@gmail.com>
Reviewed-by: NChris Packham <judge.packham@gmail.com>

arch/arm/dts/armada-388-gp.dts

@@ -72,6 +72,8 @@
 				pinctrl-0 = <&spi0_pins>;
 				status = "okay";
 				u-boot,dm-pre-reloc;
+				#address-cells = <1>;
+				#size-cells = <0>;
 
 				spi-flash@0 {
 					u-boot,dm-pre-reloc;