ide: Fix cs5535 driver accessing beyond array boundary

The cs5535 uses an incorrect construct to access the other drive of a pair,
causing it to access beyond an array boundary on the secondary interface.

This fixes it by using the new ide_get_paired_drive() helper instead.

Bart: patch description fixes

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andrew Morton <akpm@osdl.org>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/pci/cs5535.c

@@ -84,7 +84,7 @@ static void cs5535_set_speed(ide_drive_t *drive, const u8 speed)
 
 	/* Set the PIO timings */
 	if ((speed & XFER_MODE) == XFER_PIO) {
-		ide_drive_t *pair = &drive->hwif->drives[drive->dn ^ 1];
+		ide_drive_t *pair = ide_get_paired_drive(drive);
 		u8 cmd, pioa;
 
 		cmd = pioa = speed - XFER_PIO_0;