dt-bindings: iio: magnetometer: Add ak09118

Document asahi-kasei,ak09918 compatible as a fallback compatible,
ak09918 is register compatible with ak09912.
Signed-off-by: Danila Tikhonov <danila@jiaxyga.com>
Signed-off-by: Barnabás Czémán <barnabas.czeman@mainlining.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240819-ak09918-v4-3-f0734d14cfb9@mainlining.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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

@@ -18,6 +18,10 @@ properties:
           - asahi-kasei,ak09911
           - asahi-kasei,ak09912
           - asahi-kasei,ak09916
+      - items:
+          # ak09918 is register compatible with ak09912.
+          - const: asahi-kasei,ak09918
+          - const: asahi-kasei,ak09912
       - enum:
           - ak8975
           - ak8963