f2fs: keep lazytime on remount

This patch fixes losing lazytime when remounting f2fs.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1550,6 +1550,7 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 		(test_opt(sbi, POSIX_ACL) ? SB_POSIXACL : 0);
 
 	limit_reserve_root(sbi);
+	*flags = (*flags & ~SB_LAZYTIME) | (sb->s_flags & SB_LAZYTIME);
 	return 0;
 restore_gc:
 	if (need_restart_gc) {