iio: adc: ad7380: fix adi,gain-milli property parsing

Change the data type of the "adi,gain-milli" property from u32 to u16.
The devicetree binding specifies it as uint16, so we need to read it as
such to avoid an -EOVERFLOW error when parsing the property.

Fixes: c904e6d ("iio: adc: ad7380: add support for adaq4370-4 and adaq4380-4")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250619-iio-adc-ad7380-fix-adi-gain-milli-parsing-v1-1-4c27fb426860@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
(cherry picked from commit 24fa698)

Author: dlech

drivers/iio/adc/ad7380.c

@@ -1997,8 +1997,9 @@ static int ad7380_probe(struct spi_device *spi)
 
 	if (st->chip_info->has_hardware_gain) {
 		device_for_each_child_node_scoped(dev, node) {
-			unsigned int channel, gain;
+			unsigned int channel;
 			int gain_idx;
+			u16 gain;
 
 			ret = fwnode_property_read_u32(node, "reg", &channel);
 			if (ret)
@@ -2010,7 +2011,7 @@ static int ad7380_probe(struct spi_device *spi)
 						     "Invalid channel number %i\n",
 						     channel);
 
-			ret = fwnode_property_read_u32(node, "adi,gain-milli",
+			ret = fwnode_property_read_u16(node, "adi,gain-milli",
 						       &gain);
 			if (ret && ret != -EINVAL)
 				return dev_err_probe(dev, ret,