dt-bindings: iio: adc: ad7380: fix ad7380-4 reference supply

ad7380-4 is the only device from ad738x family that doesn't have an
internal reference. Moreover its external reference is called REFIN in
the datasheet while all other use REFIO as an optional external
reference. If refio-supply is omitted the internal reference is
used.

Fix the binding by adding refin-supply and makes it required for
ad7380-4 only.

Fixes: 1a291cc8ee ("dt-bindings: iio: adc: ad7380: add support for ad738x-4 4 channels variants")
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Link: https://patch.msgid.link/20241022-ad7380-fix-supplies-v3-1-f0cefe1b7fa6@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml

@@ -67,6 +67,10 @@ properties:
       A 2.5V to 3.3V supply for the external reference voltage. When omitted,
       the internal 2.5V reference is used.
 
+  refin-supply:
+    description:
+      A 2.5V to 3.3V supply for external reference voltage, for ad7380-4 only.
+
   aina-supply:
     description:
       The common mode voltage supply for the AINA- pin on pseudo-differential
@@ -135,6 +139,23 @@ allOf:
         ainc-supply: false
         aind-supply: false
 
+  # ad7380-4 uses refin-supply as external reference.
+  # All other chips from ad738x family use refio as optional external reference.
+  # When refio-supply is omitted, internal reference is used.
+  - if:
+      properties:
+        compatible:
+          enum:
+            - adi,ad7380-4
+    then:
+      properties:
+        refio-supply: false
+      required:
+        - refin-supply
+    else:
+      properties:
+        refin-supply: false
+
 examples:
   - |
     #include <dt-bindings/interrupt-controller/irq.h>