f2fs: fix to handle error in f2fs_disable_checkpoint()

In f2fs_disable_checkpoint(), it needs to detect and propagate error
number returned from f2fs_write_checkpoint().
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1504,9 +1504,12 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 	mutex_lock(&sbi->gc_mutex);
 	cpc.reason = CP_PAUSE;
 	set_sbi_flag(sbi, SBI_CP_DISABLED);
-	f2fs_write_checkpoint(sbi, &cpc);
+	err = f2fs_write_checkpoint(sbi, &cpc);
+	if (err)
+		goto out_unlock;
 
 	sbi->unusable_block_count = 0;
+out_unlock:
 	mutex_unlock(&sbi->gc_mutex);
 restore_flag:
 	sbi->sb->s_flags = s_flags;	/* Restore MS_RDONLY status */