scsi: aacraid: replace aac_flush_ios() with midlayer helper

Use the midlayer helper scsi_host_complete_all_commands() to flush all
outstanding commands.

Link: https://lore.kernel.org/r/20200228075318.91255-7-hare@suse.de


Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Balsundar P <balsundar.p@microchip.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>