configfs: Convert subsystem semaphore to mutex

Convert the su_sem member of struct configfs_subsystem to a struct
mutex, as that's what it is. Also convert all the users and update
Documentation/configfs.txt and Documentation/configfs_example.c
accordingly.

[ Conflict in fs/dlm/config.c with commit
  3168b0780d06ace875696f8a648d04d6089654e5 manually resolved. --Mark ]

Inspired-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
diff --git a/fs/ocfs2/cluster/nodemanager.c b/fs/ocfs2/cluster/nodemanager.c
index 9f5ad0f..48b77d1 100644
--- a/fs/ocfs2/cluster/nodemanager.c
+++ b/fs/ocfs2/cluster/nodemanager.c
@@ -934,7 +934,7 @@
 		goto out_sysctl;
 
 	config_group_init(&o2nm_cluster_group.cs_subsys.su_group);
-	init_MUTEX(&o2nm_cluster_group.cs_subsys.su_sem);
+	mutex_init(&o2nm_cluster_group.cs_subsys.su_mutex);
 	ret = configfs_register_subsystem(&o2nm_cluster_group.cs_subsys);
 	if (ret) {
 		printk(KERN_ERR "nodemanager: Registration returned %d\n", ret);