Next 5 chunks prepare cleanup of scsi_get_request_dev().  Namely,
scsi_disk/scsi_cd/... get a new field - pointer to Scsi_Device_Template.
It is initialized with address of that driver's template.  sr.c and sd.c
have disk->private_data pointing to that field (instead of pointing to
entire structure).  osst.c, st.c and sg.c get gendisk - allocated, but
not registered (obviously) with ->private_name set in the same way.  When
they set ->rq_dev, they also set ->rq_disk.
	This chunk does it for osst.c