[SCSI] Fix oops caused by queue refcounting failure

In certain circumstances, we can get an oops from a torn down device.
Most notably this is from CD roms trying to call scsi_ioctl.  The root
cause of the problem is the fact that after scsi_remove_device() has
been called, the queue is fully torn down.  This is actually wrong
since the queue can be used until the sdev release function is called.
Therefore, we add an extra reference to the queue which is released in
sdev->release, so the queue always exists.

Reported-by: Parag Warudkar <parag.lkml@gmail.com>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <jbottomley@parallels.com>