iio: adf4030: Add adf4030_fwnode_xlate() for non-1:1 map

Adds method to map the fwnode_reference_args->args[0] value to the
iio_channel index, instead of relying on __fwnode_iio_simple_xlate()
that supports only 1:1 mapped channels. Allows to not describe and skip
channels in the devicetree.

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Author: gastmaier

drivers/iio/frequency/adf4030.c

@@ -887,10 +887,24 @@ static int adf4030_read_avail(struct iio_dev *indio_dev,
 	}
 }
 
+static int adf4030_fwnode_xlate(struct iio_dev *indio_dev,
+				const struct fwnode_reference_args *iiospec)
+{
+	struct adf4030_state *st = iio_priv(indio_dev);
+
+	for (int i = 0; i < st->num_channels; i++) {
+		if (st->channels[i].num == iiospec->args[0])
+			return i;
+	}
+
+	return -EINVAL;
+}
+
 static const struct iio_info adf4030_iio_info = {
 	.read_raw = &adf4030_read_raw,
 	.write_raw = &adf4030_write_raw,
 	.read_avail = &adf4030_read_avail,
+	.fwnode_xlate = &adf4030_fwnode_xlate,
 	.debugfs_reg_access = &adf4030_reg_access,
 };