scsi: aacraid: change wait_sem to a completion

The wait_sem member is used like a completion, so we should
use the respective API. The behavior is unchanged.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Dave Carroll <david.carroll@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>