[SCSI] ibmmca: fix buffer overflow

Allows i == IM_MAX_HOSTS, which is out of range.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>