dt-bindings: iio: adc: Add burn-out current properties

Some ADCs incorporate burn-out current sources that provide current to
the channel's input pins for open-circuit or short-circuit detection.

Signed-off-by: Kurt Borja <kuurtb@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: David Lechner (TI) <dlechner@baylibre.com>
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>

Documentation/devicetree/bindings/iio/adc/adc.yaml

@@ -101,6 +101,11 @@ properties:
       sources. The index in the array corresponds to the same index in the
       excitation-channels array.
 
+  burn-out-current-nanoamp:
+    description:
+      Burn-out current sources provide current to the channel's input pins for
+      open-circuit or short-circuit detection.
+
 anyOf:
   - oneOf:
       - required: