imsm: don't check raid1 chunk size

imsm: don't check raid1 chunk size

mdadm -C /dev/md/r1d2n1s0-5 -amd -l1  --size 5242880 -n 2 /dev/sdb /dev/sdc  -R -f -v -c 64
mdadm: chunk size ignored for this level
mdadm: super0.90 cannot open /dev/sdb: Device or resource busy
mdadm: super1.x cannot open /dev/sdb: Device or resource busy
mdadm: platform does not support a chunk size of: 0
mdadm: device /dev/sdb not suitable for any style of array

Reported-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
Tested-by: Jacek Danecki <jacek.danecki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>