scsi_debug: review fixes for scsi-mq changes

This series of patches is a result of feedback from the large patch titled "[PATCH v2] scsi_debug: support scsi-mq, queues and locks" sent to the list on 20140707. That patch is now in Christoph's drivers-for-3.17 repository.

1/3: scsi_cmnd->cmnd check and casts unnecessary 2/3: give unit attention and other errors precedence over TSF 3/3: bump inquiry version to SPC-4, update version descriptors

Thanks Doug,

all the patches look good to me.

Thanks,

I've applied all three patches to the driver-for-3.18 branch.