ARM: mvebu: fix unit address on armada-390-db flash

The unit address needs to be changed to match the reg property:

arch/arm/boot/dts/marvell/armada-390-db.dts:84.10-106.4: Warning (spi_bus_reg): /soc/spi@10680/flash@1: SPI bus unit address format error, expected "0"
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/boot/dts/marvell/armada-390-db.dts

@@ -81,7 +81,7 @@ &spi1 {
 	pinctrl-0 = <&spi1_pins>;
 	pinctrl-names = "default";
 
-	flash@1 {
+	flash@0 {
 		#address-cells = <1>;
 		#size-cells = <1>;
 		compatible = "n25q128a13",