remove stale comment from <linux/hdreg.h>

HDIO_GET_IDENTITY returns 256 words currently.

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

include/linux/hdreg.h

@@ -511,7 +511,6 @@ struct hd_driveid {
 	unsigned short	words69_70[2];	/* reserved words 69-70
 					 * future command overlap and queuing
 					 */
-	/* HDIO_GET_IDENTITY currently returns only words 0 through 70 */
 	unsigned short	words71_74[4];	/* reserved words 71-74
 					 * for IDENTIFY PACKET DEVICE command
 					 */