hpsa: fix rmmod issues

The driver is calling hpsa_shutdown before calling scsi_remove_host.
hpsa_shutdown is disabling interrupts.

scsi_remove_host can trigger I/O operations, such as
SYNCHRONIZE CACHE when multipath is enabled which hang the system.

Call scsi_remove_host before calling hpsa_shutdown.

Reviewed-by: Kevin Barnett <kevin.barnett@pmcs.com>
Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>