scsi_host_lookup — get a reference to a Scsi_Host by host no
| struct Scsi_Host * scsi_host_lookup ( | unsigned short hostnum ); | 
A pointer to located Scsi_Host or NULL.
   The caller must do a scsi_host_put to drop the reference
   that scsi_host_get took. The put_device below dropped
   the reference from class_find_device.