ARM: dts: mxs: add #io-channel-cells to mx28 lradc

Adding #io-channel-cells property to lradc allows us to use the lradc as
an iio provider.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28.dtsi

@@ -997,6 +997,7 @@ lradc: lradc@80050000 {
 						20 21 22 23 24 25>;
 				status = "disabled";
 				clocks = <&clks 41>;
+				#io-channel-cells = <1>;
 			};
 
 			spdif: spdif@80054000 {