dm-raid: don't set io_min and io_opt for raid1

dm-raid: don't set io_min and io_opt for raid1

These commands
 modprobe brd rd_size=1048576
 vgcreate vg /dev/ram*
 lvcreate -m4 -L10 -n lv vg
trigger the following warnings:
device-mapper: table: 252:10: adding target device (start sect 0 len 24576) caused an alignment inconsistency
device-mapper: table: 252:10: adding target device (start sect 0 len 24576) caused an alignment inconsistency

The warnings are caused by the fact that io_min is 512 and physical block
size is 4096.

If there's chunk-less raid, such as raid1, io_min shouldn't be set to zero
because it would be raised to 512 and it would trigger the warning.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: stable@vger.kernel.org