ARM: dts: imx7s: Specify #io-channel-cells in ADC nodes

Specify #io-channel-cells in ADC nodes. Needed to be able to reference
them by phandle.

Signed-off-by: Andrey Smirnov <[e-mail]>
Cc: Shawn Guo <[e-mail]>
Cc: Chris Healy <[e-mail]>
Cc: Andrew Lunn <[e-mail]>
Cc: Fabio Estevam <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx7s.dtsi

···
 				interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;
 				clocks = <&clks IMX7D_ADC_ROOT_CLK>;
 				clock-names = "adc";
+				#io-channel-cells = <1>;
 				status = "disabled";
 			};
 
···
 				interrupts = <GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>;
 				clocks = <&clks IMX7D_ADC_ROOT_CLK>;
 				clock-names = "adc";
+				#io-channel-cells = <1>;
 				status = "disabled";
 			};