scsi: sun3_scsi: Use scsi_cmd_to_rq() instead of scsi_cmnd.request

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

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bart Van Assche <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/sun3_scsi.c

···
 {
 	int wanted_len = cmd->SCp.this_residual;
 
-	if (wanted_len < DMA_MIN_SIZE || blk_rq_is_passthrough(cmd->request))
+	if (wanted_len < DMA_MIN_SIZE || blk_rq_is_passthrough(scsi_cmd_to_rq(cmd)))
 		return 0;
 
 	return wanted_len;