Rather than traversing all outstanding commands manually, use the
scsi_host_complete_all_commands() helper to terminate all commands during
reset.  With that we can drop the cmd_list usage from the midlayer.

Link: https://lore.kernel.org/r/20200228075318.91255-4-hare@suse.deReviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>