iio: adc: ad7768-1: use device_* to iterate over device child nodes

Drop the manual access to the fwnode of the device to iterate over its
child nodes. `device_for_each_child_node` macro provides direct access
to the child nodes, and given that they are only required within the
loop, the scoped variant of the macro can be used.

Use the `device_for_each_child_node_scoped` macro to iterate over the
direct child nodes of the device.
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240801-device_child_node_access-v1-2-ddfa21bef6f2@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7768-1.c

@@ -544,13 +544,10 @@ static int ad7768_set_channel_label(struct iio_dev *indio_dev,
 {
 	struct ad7768_state *st = iio_priv(indio_dev);
 	struct device *device = indio_dev->dev.parent;
-	struct fwnode_handle *fwnode;
-	struct fwnode_handle *child;
 	const char *label;
 	int crt_ch = 0;
 
-	fwnode = dev_fwnode(device);
-	fwnode_for_each_child_node(fwnode, child) {
+	device_for_each_child_node_scoped(device, child) {
 		if (fwnode_property_read_u32(child, "reg", &crt_ch))
 			continue;