powerpc: Fix new-world powermac detection

My G5 was being reported as an OldWorld in /proc/cpuinfo, which is
obviously not right... :)

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/platforms/powermac/setup.c b/arch/powerpc/platforms/powermac/setup.c
index 72cd503..6f62af5 100644
--- a/arch/powerpc/platforms/powermac/setup.c
+++ b/arch/powerpc/platforms/powermac/setup.c
@@ -317,7 +317,9 @@
 	}
 
 	/* See if newworld or oldworld */
-	ic = of_find_node_by_name(NULL, "interrupt-controller");
+	for (ic = NULL; (ic = of_find_all_nodes(ic)) != NULL; )
+		if (get_property(ic, "interrupt-controller", NULL))
+			break;
 	pmac_newworld = (ic != NULL);
 	if (ic)
 		of_node_put(ic);