dt-bindings:iio:dac:ti,dac5571 yaml conversion.

A few tweaks in this conversion.
* The example didn't have the I2C address of 4C in the node name so
  fixed that.
* The reference voltage in the txt file is an optional binding, but
  the driver is making use of it to provide the scaling of the output
  channels.  As such I have made it required going forwards.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Sean Nyekjaer <sean@geanix.com>
Link: https://lore.kernel.org/r/20201031134110.724233-13-jic23@kernel.org

Documentation/devicetree/bindings/iio/dac/ti,dac5571.txt

-* Texas Instruments DAC5571 Family
-
-Required properties:
- - compatible: Should contain
-    "ti,dac5571"
-    "ti,dac6571"
-    "ti,dac7571"
-    "ti,dac5574"
-    "ti,dac6574"
-    "ti,dac7574"
-    "ti,dac5573"
-    "ti,dac6573"
-    "ti,dac7573"
- - reg: Should contain the DAC I2C address
-
-Optional properties:
- - vref-supply: The regulator supply for DAC reference voltage
-
-Example:
-dac@0 {
-	compatible = "ti,dac5571";
-	reg = <0x4C>;
-	vref-supply = <&vdd_supply>;
-};

Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/dac/ti,dac5571.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments DAC5571 Family
+
+maintainers:
+  - Sean Nyekjaer <sean@geanix.com>
+
+properties:
+  compatible:
+    enum:
+      - ti,dac5571
+      - ti,dac6571
+      - ti,dac7571
+      - ti,dac5574
+      - ti,dac6574
+      - ti,dac7574
+      - ti,dac5573
+      - ti,dac6573
+      - ti,dac7573
+
+  reg:
+    maxItems: 1
+
+  vref-supply:
+    description:
+      Reference voltage must be supplied to establish the scaling of the
+      output voltage.
+
+required:
+  - compatible
+  - reg
+  - vref-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        dac@4c {
+            compatible = "ti,dac5571";
+            reg = <0x4C>;
+            vref-supply = <&vdd_supply>;
+        };
+    };
+...