ARM: dts: vf610-bk4: fix incorrect #address-cells for dspi3

The dspi3 is used as slave controller on vf610-bk4, and the default
'#address-cells = <1>;' setting in vfxxx.dtsi causes the following DTC
warning.

  DTC     arch/arm/boot/dts/vf610-bk4.dtb
../arch/arm/boot/dts/vfxxx.dtsi:550.24-563.6: Warning (spi_bus_bridge): /soc/aips-bus@40080000/spi@400ad000: incorrect #address-cells for SPI bus
  also defined at ../arch/arm/boot/dts/vf610-bk4.dts:107.8-119.3
arch/arm/boot/dts/vf610-bk4.dtb: Warning (spi_bus_reg): Failed prerequisite 'spi_bus_bridge'

For spi device used as slave controller, '#address-cells' should be 0.
Let's overwrite the property in vf610-bk4.dts to fix the warning.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/vf610-bk4.dts

@@ -110,11 +110,11 @@ &dspi3 {
 	bus-num = <3>;
 	status = "okay";
 	spi-slave;
+	#address-cells = <0>;
 
-	slave@0 {
+	slave {
 		compatible = "lwn,bk4";
 		spi-max-frequency = <30000000>;
-		reg = <0>;
 	};
 };