Revert "[SCSI] fix bsg queue oops with iscsi logout"

This reverts commit 4b6f5b3a

.

bsg takes a reference to the underlying generic device, so it's
impossible to unregister bsg in the device release routine.

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