dt-bindings: iio: st-sensors: Re-add IIS2MDC magnetometer

"iio: st-sensors: Update ST Sensor bindings" accidentially dropped
the compatible for the IIS2MDC magnetometer.

Fixes: 0cd7114 ("iio: st-sensors: Update ST Sensor bindings")
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20241129-stmagdt-v1-1-963f0347fb0a@geanix.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: sknsean

Documentation/devicetree/bindings/iio/st,st-sensors.yaml

@@ -65,6 +65,7 @@ properties:
           - st,lsm9ds0-gyro
       - description: STMicroelectronics Magnetometers
         enum:
+          - st,iis2mdc
           - st,lis2mdl
           - st,lis3mdl-magn
           - st,lsm303agr-magn