device-dax: Drop register_filesystem()

The device-dax fs is only there to allocate a common inode for each
device-node that refers to the same device by major:minor. It is
otherwise not user mountable and need not be displayed in
/proc/filesystems.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/dax/super.c

@@ -630,10 +630,6 @@ static int dax_fs_init(void)
 	if (!dax_cache)
 		return -ENOMEM;
 
-	rc = register_filesystem(&dax_fs_type);
-	if (rc)
-		goto err_register_fs;
-
 	dax_mnt = kern_mount(&dax_fs_type);
 	if (IS_ERR(dax_mnt)) {
 		rc = PTR_ERR(dax_mnt);
@@ -644,8 +640,6 @@ static int dax_fs_init(void)
 	return 0;
 
  err_mount:
-	unregister_filesystem(&dax_fs_type);
- err_register_fs:
 	kmem_cache_destroy(dax_cache);
 
 	return rc;
@@ -654,7 +648,6 @@ static int dax_fs_init(void)
 static void dax_fs_exit(void)
 {
 	kern_unmount(dax_mnt);
-	unregister_filesystem(&dax_fs_type);
 	kmem_cache_destroy(dax_cache);
 }