scsi: qla1280: Use scsi_cmd_to_rq() instead of scsi_cmnd.request

Prepare for removal of the request pointer by using scsi_cmd_to_rq()
instead. Remove the unused CMD_REQUEST() macro. This patch does not change
any functionality.

Link: https://lore.kernel.org/r/20210809230355.8186-38-bvanassche@acm.org
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>