[SCSI] bsg: make class backlinks

Currently, bsg doesn't make class backlinks (a process whereby you'd get
a link to bsg in the device directory in the same way you get one for
sg).  This is because the bsg device is uninitialised, so the class
device has nothing it can attach to.  The fix is to make the bsg device
point to the cdevice of the entity creating the bsg, necessitating
changing the bsg_register_queue() prototype into a form that takes the
generic device.

Acked-by: FUJITA Tomonori <tomof@acm.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>