iio: core: Convert to use firmware node handle instead of OF node

Switch the IIO core to use firmware node handle instead of OF node.
This will allow to get label from firmware on non-OF systems.

Note, this doesn't change of_iio_*() APIs for now.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220413180202.19220-1-andriy.shevchenko@linux.intel.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-core.c

@@ -1907,20 +1907,22 @@ static const struct iio_buffer_setup_ops noop_ring_setup_ops;
 int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
 {
 	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
-	const char *label;
+	struct fwnode_handle *fwnode;
 	int ret;
 
 	if (!indio_dev->info)
 		return -EINVAL;
 
 	iio_dev_opaque->driver_module = this_mod;
-	/* If the calling driver did not initialize of_node, do it here */
-	if (!indio_dev->dev.of_node && indio_dev->dev.parent)
-		indio_dev->dev.of_node = indio_dev->dev.parent->of_node;
 
-	label = of_get_property(indio_dev->dev.of_node, "label", NULL);
-	if (label)
-		indio_dev->label = label;
+	/* If the calling driver did not initialize firmware node, do it here */
+	if (dev_fwnode(&indio_dev->dev))
+		fwnode = dev_fwnode(&indio_dev->dev);
+	else
+		fwnode = dev_fwnode(indio_dev->dev.parent);
+	device_set_node(&indio_dev->dev, fwnode);
+
+	fwnode_property_read_string(fwnode, "label", &indio_dev->label);
 
 	ret = iio_check_unique_scan_index(indio_dev);
 	if (ret < 0)