When array size is not aligned to copy area, number of migration unit
is increased in init_migr_record_imsm():7665 to reshape whole array.
During calculation of last migration unit, this should be in mind also,
otherwise checkpoint (max-1) is always written and reshape
is never finished in mdadm.
Signed-off-by: Adam Kwolek <adam.kwolek@intel.com> Signed-off-by: NeilBrown <neilb@suse.de>