scsi: fas216: Stop using scsi_cmnd.scsi_done

Store the completion callback pointer in struct fas216_cmd_priv instead of
in struct scsi_cmnd. This patch prepares for removal of the scsi_done
member from struct scsi_cmnd.

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/arm/fas216.c

···
 	 * correctly by fas216_std_done.
 	 */
 	scsi_eh_restore_cmnd(SCpnt, &info->ses);
-	SCpnt->scsi_done(SCpnt);
+	fas216_cmd_priv(SCpnt)->scsi_done(SCpnt);
 }
 
 /**
···
 	}
 
 done:
-	if (SCpnt->scsi_done) {
-		SCpnt->scsi_done(SCpnt);
+	if (fas216_cmd_priv(SCpnt)->scsi_done) {
+		fas216_cmd_priv(SCpnt)->scsi_done(SCpnt);
 		return;
 	}
 
···
 	fas216_log_command(info, LOG_CONNECT, SCpnt,
 			   "received command (%p)", SCpnt);
 
-	SCpnt->scsi_done = done;
+	fas216_cmd_priv(SCpnt)->scsi_done = done;
 	SCpnt->host_scribble = (void *)fas216_std_done;
 	SCpnt->result = 0;