_Now_ we can clean the scsi_get_request_dev() up.  Indeed, for
any SCSI request we either have ->rq_dev == NODEV and ->rq_disk == NULL
or ->rq_disk->private_data points to address of template in question.
IOW, scsi_get_request_dev() becomes simply
{
	struct gendisk *p = req->rq_disk;
	return p ? *(struct Scsi_Device_Template **)p->private_data : NULL;
}
and that allows to kill ->max_major, ->min_major and ->major in
Scsi_Device_Template, along with the last non-trivial use of ->rq_dev.