ext2: fix return values on parse_options() failure

parse_options() in ext2 should return 0 when parse the mount options fails.

Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>