Unlock vfsmount_lock in do_umount

By the commit
	b3e19d9 2011-01-07 fs: scale mntget/mntput
vfsmount_lock was introduced around testing mnt_count.
Fix the mis-typed 'unlock'

Signed-off-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namespace.c

@@ -1244,7 +1244,7 @@ static int do_umount(struct vfsmount *mnt, int flags)
 		 */
 		br_write_lock(vfsmount_lock);
 		if (mnt_get_count(mnt) != 2) {
-			br_write_lock(vfsmount_lock);
+			br_write_unlock(vfsmount_lock);
 			return -EBUSY;
 		}
 		br_write_unlock(vfsmount_lock);