[POWERPC] Fix ohare IDE irq workaround on old powermacs

Looks like a workaround for old bogus OF bitrot...  This fixes it and
hence fixes boot on some performa machines.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

drivers/ide/ppc/pmac.c

@@ -1326,7 +1326,7 @@ pmac_ide_macio_attach(struct macio_dev *mdev, const struct of_device_id *match)
 	if (macio_irq_count(mdev) == 0) {
 		printk(KERN_WARNING "ide%d: no intrs for device %s, using 13\n",
 			i, mdev->ofdev.node->full_name);
-		irq = 13;
+		irq = irq_create_mapping(NULL, 13);
 	} else
 		irq = macio_irq(mdev, 0);