[libata] ahci_platform: fix DT probing

The change in commit 904c04fe "ahci_platform: Add the board_ids..."
doesn't work for the DT probing case as platform_get_device_id returns
NULL. Pick the default ahci_port_info in this case.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Cc: Richard Zhu <richard.zhu@linaro.org>
Cc: linux-ide@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci_platform.c

@@ -67,7 +67,7 @@ static int __init ahci_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct ahci_platform_data *pdata = dev_get_platdata(dev);
 	const struct platform_device_id *id = platform_get_device_id(pdev);
-	struct ata_port_info pi = ahci_port_info[id->driver_data];
+	struct ata_port_info pi = ahci_port_info[id ? id->driver_data : 0];
 	const struct ata_port_info *ppi[] = { &pi, NULL };
 	struct ahci_host_priv *hpriv;
 	struct ata_host *host;