ubifs: fix to check error code of register_shrinker

register_shrinker() in ubifs_init() can fail due to fail to call kzalloc.
This patch fixes to check the return value of register_shrinker, otherwise
our shrinker may be unregistered after ubifs initialized successfully.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/super.c

@@ -2245,7 +2245,9 @@ static int __init ubifs_init(void)
 	if (!ubifs_inode_slab)
 		return -ENOMEM;
 
-	register_shrinker(&ubifs_shrinker_info);
+	err = register_shrinker(&ubifs_shrinker_info);
+	if (err)
+		goto out_slab;
 
 	err = ubifs_compressors_init();
 	if (err)
@@ -2269,6 +2271,7 @@ out_compr:
 	ubifs_compressors_exit();
 out_shrinker:
 	unregister_shrinker(&ubifs_shrinker_info);
+out_slab:
 	kmem_cache_destroy(ubifs_inode_slab);
 	return err;
 }