swap_prefetch: Convert nr_dirty to zone count

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.17-rc6-cl/mm/swap_prefetch.c
===================================================================
--- linux-2.6.17-rc6-cl.orig/mm/swap_prefetch.c	2006-06-12 12:55:29.984174144 -0700
+++ linux-2.6.17-rc6-cl/mm/swap_prefetch.c	2006-06-12 12:55:33.862840200 -0700
@@ -393,7 +393,7 @@ static int prefetch_suitable(void)
 		limit = node_page_state(node, NR_MAPPED) +
 			node_page_state(node, NR_ANON) +
 			node_page_state(node, NR_SLAB) +
-			ps.nr_dirty +
+			node_page_state(node, NR_DIRTY) +
 			ps.nr_unstable + total_swapcache_pages;
 		if (limit > ns->prefetch_watermark) {
 			node_clear(node, sp_stat.prefetch_nodes);