libata: initialize port_task when !CONFIG_ATA_SFF

ap->port_task was not initialized if !CONFIG_ATA_SFF later triggering
lockdep warning.  Make sure it's initialized.

Reported by Larry Finger.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-core.c

@@ -5373,6 +5373,8 @@ struct ata_port *ata_port_alloc(struct ata_host *host)
 
 #ifdef CONFIG_ATA_SFF
 	INIT_DELAYED_WORK(&ap->port_task, ata_pio_task);
+#else
+	INIT_DELAYED_WORK(&ap->port_task, NULL);
 #endif
 	INIT_DELAYED_WORK(&ap->hotplug_task, ata_scsi_hotplug);
 	INIT_WORK(&ap->scsi_rescan_task, ata_scsi_dev_rescan);