dt-bindings: iio: adc: sd-modulator: fix io-channel-cells

io-channel-cells should be <0> since sigma delta modulator exports only
one channel, as described in ../iio/iio-bindings.txt "IIO providers"
section. Only the phandle is necessary for IIO consumers in this case.

Fixes: af11143 ("IIO: Add DT bindings for sigma delta adc modulator")

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.txt

@@ -3,11 +3,11 @@ Device-Tree bindings for sigma delta modulator
 Required properties:
 - compatible: should be "ads1201", "sd-modulator". "sd-modulator" can be use
 	as a generic SD modulator if modulator not specified in compatible list.
-- #io-channel-cells = <1>: See the IIO bindings section "IIO consumers".
+- #io-channel-cells = <0>: See the IIO bindings section "IIO consumers".
 
 Example node:
 
 	ads1202: adc@0 {
 		compatible = "sd-modulator";
-		#io-channel-cells = <1>;
+		#io-channel-cells = <0>;
 	};