dt-bindings: iio: adc: adi,max11410: fix yaml syntax

The adi,max11410.yaml file has a syntax error that causes it to be
ignored with the following warning when running `make dt_binding_check`:

    /home/david/work/linux/Documentation/devicetree/bindings/iio/adc/adi,max11410.yaml: ignoring, error parsing file

Fixes: d3f83f5 ("dt-bindings: iio: adc: add adi,max11410.yaml")
Signed-off-by: David Lechner <dlechner@baylibre.com>

Author: dlech

Documentation/devicetree/bindings/iio/adc/adi,max11410.yaml

@@ -41,8 +41,10 @@ properties:
     const: 0
 
   avdd-supply:
-    description: Optional avdd supply. Used as reference when no explicit reference \
-upplied. +
+    description:
+      Optional avdd supply. Used as reference when no explicit reference
+      is supplied.
+
   vref0p-supply:
     description: vref0p supply can be used as reference for conversion.