dt-bindings: iio: dac: ad5770r: Add vendor to compatible string

The compatible string in the example misses the vendor information.

Pass the "adi" vendor to fix it.
Signed-off-by: NFabio Estevam <festevam@gmail.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NRob Herring <robh@kernel.org>

Documentation/devicetree/bindings/iio/dac/adi,ad5770r.yaml

@@ -144,7 +144,7 @@ examples:
                 #size-cells = <0>;
 
                 ad5770r@0 {
-                        compatible = "ad5770r";
+                        compatible = "adi,ad5770r";
                         reg = <0>;
                         spi-max-frequency = <1000000>;
                         vref-supply = <&vref>;