software node: Fix node registration

Software node can not be registered before its parent.

Fixes: 80488a6b ("software node: Add support for static node descriptors")
Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/swnode.c

@@ -938,6 +938,9 @@ int software_node_register(const struct software_node *node)
 	if (software_node_to_swnode(node))
 		return -EEXIST;
 
+	if (node->parent && !parent)
+		return -EINVAL;
+
 	return PTR_ERR_OR_ZERO(swnode_register(node, parent, 0));
 }
 EXPORT_SYMBOL_GPL(software_node_register);