[SCSI] NCR5380: Fix bugs and canonicalize irq handler usage

* Always pass the same value to free_irq() that we pass to
  request_irq().  This fixes several bugs.

* Always call NCR5380_intr() with 'irq' and 'dev_id' arguments.

  Note, scsi_falcon_intr() is the only case now where dev_id is not the
  scsi_host.

* Always pass Scsi_Host to request_irq().  For most cases, the drivers
  already did so, and I merely neated the source code line.  In other
  cases, either NULL or a non-sensical value was passed, verified to be
  unused, then changed to be Scsi_Host in anticipation of the future.

In addition to the bugs fixes, this change makes the interface usage
consistent, which in turn enables the possibility of directly
referencing Scsi_Host from all NCR5380_intr() invocations.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>