scsi: scsi_debug: Use blk_mq_tagset_busy_iter() in stop_all_queued()

Instead of iterating all deferred commands in the submission queue
structures, use blk_mq_tagset_busy_iter(), which is a standard API for
this.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20230327074310.1862889-9-john.g.garry@oracle.com


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>