libata: -ENODEV during prereset isn't an error

During prereset, -ENODEV return from ata_wait_ready() is not an error.
This causes unnecessary bug message on controllers which uses 0xff to
indicate empty port.  Fix it.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -3368,7 +3368,7 @@ int ata_std_prereset(struct ata_port *ap, unsigned long deadline)
 	 */
 	if (!(ap->flags & ATA_FLAG_SKIP_D2H_BSY) && !ata_port_offline(ap)) {
 		rc = ata_wait_ready(ap, deadline);
-		if (rc) {
+		if (rc && rc != -ENODEV) {
 			ata_port_printk(ap, KERN_WARNING, "device not ready "
 					"(errno=%d), forcing hardreset\n", rc);
 			ehc->i.action |= ATA_EH_HARDRESET;