powerpc/numa: Avoid stupid uninitialized warning from gcc

Newer gcc are being a bit blind here (it's pretty obvious we don't
reach the code path using the array if we haven't initialized the
pointer) but none of that is performance critical so let's just
silence it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/numa.c

@@ -639,7 +639,7 @@ static void __init parse_drconf_memory(struct device_node *memory)
 	unsigned int n, rc, ranges, is_kexec_kdump = 0;
 	unsigned long lmb_size, base, size, sz;
 	int nid;
-	struct assoc_arrays aa;
+	struct assoc_arrays aa = { .arrays = NULL };
 
 	n = of_get_drconf_memory(memory, &dm);
 	if (!n)