ide kill unused ide_cmd->special

Impact: removal of unused field

No one uses ide_cmd->special anymore.  Kill it.
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/ide.h

@@ -324,7 +324,6 @@ struct ide_cmd {
 	unsigned int		cursg_ofs;
 
 	struct request		*rq;		/* copy of request */
-	void			*special;	/* valid_t generally */
 };
 
 /* ATAPI packet command flags */