libata: no need to speed down if already at PIO0

After reset, transfer mode is always PIO0 regardless of
dev->xfer_mask.  Check dev->pio_mode before trying to slow down after
configuration failure.  This prevents bogus speed down before device
is actually configured.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-eh.c

@@ -2437,7 +2437,7 @@ static int ata_eh_handle_dev_fail(struct ata_device *dev, int err)
 		/* give it just one more chance */
 		ehc->tries[dev->devno] = min(ehc->tries[dev->devno], 1);
 	case -EIO:
-		if (ehc->tries[dev->devno] == 1) {
+		if (ehc->tries[dev->devno] == 1 && dev->pio_mode > XFER_PIO_0) {
 			/* This is the last chance, better to slow
 			 * down than lose it.
 			 */