ARM: dts: vf610-zii-dev-rev-b: fix interrupt for GPIO expander

The interrupt specification for the GPIO expander is wrong - the
expander is wired to PTB28, which is GPIO98.  GPIO98 is on gpio chip
3, not 2.

In addition, the device is missing a required property.  Interrupt
controllers must have the "interrupt-controller" property specified.
Add this.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/vf610-zii-dev-rev-b.dts

@@ -371,7 +371,8 @@ gpio6: pca9554@22 {
 		reg = <0x22>;
 		gpio-controller;
 		#gpio-cells = <2>;
-		interrupt-parent = <&gpio2>;
+		interrupt-controller;
+		interrupt-parent = <&gpio3>;
 		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
 	};
 };