dt-bindings: iio: sigma-delta-modulator: fix unit-address in example

Device tree compiler gives a warning if a device node has "@"
but no reg property.
Fix the example in iio: adc: sigma-delta-modulator.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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

@@ -7,7 +7,7 @@ Required properties:
 
 Example node:
 
-	ads1202: adc@0 {
+	ads1202: adc {
 		compatible = "sd-modulator";
 		#io-channel-cells = <0>;
 	};