net: mdio: thunder: switch to scoped device_for_each_child_node()

There has already been an issue with the handling of early exits from
device_for_each_child() in this driver, and it was solved with commit
b1de5c7 ("net: mdio: thunder: Add missing fwnode_handle_put()") by
adding a call to fwnode_handle_put() right after the loop.

That solution is valid indeed, but if a new error path with a 'return'
is added to the loop, this solution will fail. A more secure approach
is using the scoped variant of the macro, which automatically
decrements the refcount of the child node when it goes out of scope,
removing the need for explicit calls to fwnode_handle_put().

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20240930-net-device_for_each_child_node_scoped-v2-1-35f09333c1d7@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/mdio/mdio-thunder.c

@@ -23,7 +23,6 @@ static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
 				     const struct pci_device_id *ent)
 {
 	struct device_node *node;
-	struct fwnode_handle *fwn;
 	struct thunder_mdiobus_nexus *nexus;
 	int err;
 	int i;
@@ -54,7 +53,7 @@ static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
 	}
 
 	i = 0;
-	device_for_each_child_node(&pdev->dev, fwn) {
+	device_for_each_child_node_scoped(&pdev->dev, fwn) {
 		struct resource r;
 		struct mii_bus *mii_bus;
 		struct cavium_mdiobus *bus;
@@ -106,7 +105,6 @@ static int thunder_mdiobus_pci_probe(struct pci_dev *pdev,
 		if (i >= ARRAY_SIZE(nexus->buses))
 			break;
 	}
-	fwnode_handle_put(fwn);
 	return 0;
 
 err_release_regions: