[SCSI] pm80xx: fix Adaptec 71605H hang

The IO command size is 128 bytes for these new controllers as opposed to 64
for the old 8001 controller.

The Adaptec out-of-tree driver did this correctly. After comparing the two
this turned out to be the crucial difference.

So don't hardcode the IO command size, instead use pm8001_ha->iomb_size as
that is the correct value for both old and new controllers.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Anand Kumar Santhanam <AnandKumar.Santhanam@pmcs.com>
Acked-by: Jack Wang <xjtuwjp@gmail.com>
Cc: stable@vger.kernel.org      # for v3.10 and up
Signed-off-by: James Bottomley <JBottomley@Parallels.com>