dt-bindings: iio: magnetometer: asahi-kasei,ak8975 add vid reg

Driver and device-tree also use vid-supply regulator.

Fixes: 7e000fbf ("dt-bindings: iio: magnetometer: ak8975: convert format to yaml, add maintainer")
Signed-off-by: David Heidelberg <david@ixit.cz>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210913181949.83179-1-david@ixit.czSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/magnetometer/asahi-kasei,ak8975.yaml

@@ -45,6 +45,11 @@ properties:
       an optional regulator that needs to be on to provide VDD power to
       the sensor.
 
+  vid-supply:
+    description: |
+      an optional regulator that needs to be on to provide VID power to
+      the sensor.
+
   mount-matrix:
     description: an optional 3x3 mounting rotation matrix.