scsi: wd719x: Stop using the SCSI pointer

Move the DMA handle into the per-command private data instead of using the
SCSI pointer from struct scsi_cmnd. This patch prepares for removal of the
SCSI pointer from struct scsi_cmnd.

Link: https://lore.kernel.org/r/20220218195117.25689-47-bvanassche@acm.org


Cc: Ondrej Zary <linux@zary.sk>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>