workqueue: move to use bus_get_dev_root()

Direct access to the struct bus_type dev_root pointer is going away soon
so replace that with a call to bus_get_dev_root() instead, which is what
it is there for.

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230313182918.1312597-8-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/workqueue.c

@@ -5826,13 +5826,19 @@ static struct device_attribute wq_sysfs_cpumask_attr =
 
 static int __init wq_sysfs_init(void)
 {
+	struct device *dev_root;
 	int err;
 
 	err = subsys_virtual_register(&wq_subsys, NULL);
 	if (err)
 		return err;
 
-	return device_create_file(wq_subsys.dev_root, &wq_sysfs_cpumask_attr);
+	dev_root = bus_get_dev_root(&wq_subsys);
+	if (dev_root) {
+		err = device_create_file(dev_root, &wq_sysfs_cpumask_attr);
+		put_device(dev_root);
+	}
+	return err;
 }
 core_initcall(wq_sysfs_init);