f2fs: avoid redundant f2fs_flush after remount

create_flush_cmd_control will create redundant issue_flush_thread after each
remount with flush_merge option.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -555,6 +555,8 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
 
 	if (SM_I(sbi)->fcc_info) {
 		fcc = SM_I(sbi)->fcc_info;
+		if (fcc->f2fs_issue_flush)
+			return err;
 		goto init_thread;
 	}