hpsa: change devtype to unsigned

This member is used in calls to scsi_device_type.
It should be unsigned since the kernel checks for upper bounds
and it should never be negative.

Suggested-by: Tomas Henzl <thenzl@redhat.com>
Suggested-by: Hannes Reinecke <hare@suse.de>
Suggested-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>