add reference voltage regulator for adc081c

hobbitboard: add reference voltage regulator for adc081c.

Change-Id: I78d4093243903e6b69bafe60a3297fdd5de4e824
Signed-off-by: fang hui <hui.fang@freescale.com>
diff --git a/arch/arm/boot/dts/imx6ul-picosom-hobbit.dts b/arch/arm/boot/dts/imx6ul-picosom-hobbit.dts
index b3e932b..d7ab996 100644
--- a/arch/arm/boot/dts/imx6ul-picosom-hobbit.dts
+++ b/arch/arm/boot/dts/imx6ul-picosom-hobbit.dts
@@ -300,6 +300,7 @@
 	adc: adc081c {
 		compatible = "ti,adc081c";
 		reg = <0x50>;
+		vref-supply = <&reg_3p3v>;
 	};
 };