software node: Make argument to to_software_node const

to_software_node() does not need to modify the fwnode_handle it operates
on; therefore make it const. This allows passing a const fwnode_handle to
to_software_node().

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index d5b4905..9cde143 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -71,9 +71,9 @@ software_node_to_swnode(const struct software_node *node)
 	return swnode;
 }
 
-const struct software_node *to_software_node(struct fwnode_handle *fwnode)
+const struct software_node *to_software_node(const struct fwnode_handle *fwnode)
 {
-	struct swnode *swnode = to_swnode(fwnode);
+	const struct swnode *swnode = to_swnode(fwnode);
 
 	return swnode ? swnode->node : NULL;
 }