Take vfsmount_lock to fs/internal.h

no more users left outside of fs/*.c (and very few outside of
fs/namespace.c, actually)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/internal.h

@@ -70,6 +70,8 @@ extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
 
 extern void __init mnt_init(void);
 
+extern spinlock_t vfsmount_lock;
+
 /*
  * fs_struct.c
  */