[SCSI] aacraid: kmalloc/memset->kzalloc

Inspired somewhat by Vignesh Babu <vignesh.babu@wipro.com> patch to
dpt_i2o.c to replace kmalloc/memset sequences with kzalloc, doing the
same for the aacraid driver.

Signed-off-by: Mark Salyzyn <aacraid@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>