ide: struct ide_atapi_pc - remove unused fields and update documentation

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/ide.h

@@ -426,13 +426,9 @@ struct ide_atapi_pc {
 	struct idetape_bh *bh;
 	char *b_data;
 
-	/* idescsi only for now */
 	struct scatterlist *sg;
 	unsigned int sg_cnt;
 
-	struct scsi_cmnd *scsi_cmd;
-	void (*done) (struct scsi_cmnd *);
-
 	unsigned long timeout;
 };