f2fs: make exit_f2fs_fs more clear

init_f2fs_fs does:
    1) f2fs_build_trace_ios
    2) init_inodecache
    3) create_node_manager_caches
    4) create_segment_manager_caches
    5) create_checkpoint_caches
    6) create_extent_cache
    7) kset_create_and_add
    8) kobject_init_and_add
    9) register_shrinker
    10) register_filesystem
    11) f2fs_create_root_stats
    12) proc_mkdir

exit_f2fs_fs should do cleanup in the reverse order
to make the code more clear.
Signed-off-by: Tiezhu Yang <kernelpatch@126.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1926,17 +1926,17 @@ static void __exit exit_f2fs_fs(void)
 {
 	remove_proc_entry("fs/f2fs", NULL);
 	f2fs_destroy_root_stats();
-	unregister_shrinker(&f2fs_shrinker_info);
 	unregister_filesystem(&f2fs_fs_type);
+	unregister_shrinker(&f2fs_shrinker_info);
+#ifdef CONFIG_F2FS_FAULT_INJECTION
+	kobject_put(&f2fs_fault_inject);
+#endif
+	kset_unregister(f2fs_kset);
 	destroy_extent_cache();
 	destroy_checkpoint_caches();
 	destroy_segment_manager_caches();
 	destroy_node_manager_caches();
 	destroy_inodecache();
-#ifdef CONFIG_F2FS_FAULT_INJECTION
-	kobject_put(&f2fs_fault_inject);
-#endif
-	kset_unregister(f2fs_kset);
 	f2fs_destroy_trace_ios();
 }