hpsa: correct initialization order issue

The driver was calling scsi_scan_host before enabling interrupts.

This has gone unnoticed except for customers running in intx mode.
Calling scsi_scan_host before interrupts are enabled causes
"irq XX: nobody cared" messages and the driver to hang.

This patch enables interrupts before the call to scsi_scan_host.

Reported-by: Piotr Karbowski <piotr.karbowski@gmail.com>
Reviewed-by: Scott Teel <scott.teel@microsemi.com>
Reviewed-by: Kevin Barnett <kevin.barnett@microsemi.com>
Signed-off-by: Don Brace <don.brace@microsemi.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>