dm zoned: assign max_io_len correctly

The unit of max_io_len is sector instead of byte (spotted through
code review), so fix it.

Fixes: 3b1a94c8

 ("dm zoned: drive-managed zoned block device target")
Cc: stable@vger.kernel.org
Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>