f2fs: avoid freed stat information

The write_checkpoint can update stat information, so we should destroy the stat
structure after it.
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -498,7 +498,6 @@ static void f2fs_put_super(struct super_block *sb)
 	}
 	kobject_del(&sbi->s_kobj);
 
-	f2fs_destroy_stats(sbi);
 	stop_gc_thread(sbi);
 
 	/*
@@ -514,6 +513,9 @@ static void f2fs_put_super(struct super_block *sb)
 		write_checkpoint(sbi, &cpc);
 	}
 
+	/* write_checkpoint can update stat informaion */
+	f2fs_destroy_stats(sbi);
+
 	/*
 	 * normally superblock is clean, so we need to release this.
 	 * In addition, EIO will skip do checkpoint, we need this as well.