[Patch]Fix the compilation error of function addr_to_node on IA64

[Cai Fei]

Hi, all

The function addr_to_node defined in memory.stp can not work properly on 
IA64,
because the function node_start_pfn is not defined on IA64.

I made a patch as below so the function can work on all archs.
If no objection, I will commit it.

diff -Nur systemtap-20070929.orig/tapset/memory.stp systemtap-20070929/tapset/memory.stp
--- systemtap-20070929.orig/tapset/memory.stp	2007-10-03 10:48:26.000000000 +0900
+++ systemtap-20070929/tapset/memory.stp	2007-10-03 10:49:12.000000000 +0900
@@ -51,8 +51,8 @@
         int nid;
         int pfn = __pa(THIS->addr) >> PAGE_SHIFT;
         for_each_online_node(nid)
-                if ( node_start_pfn(nid) <= pfn &&
-                        pfn < (node_start_pfn(nid) +
+                if ( NODE_DATA(nid)->node_start_pfn <= pfn &&
+                        pfn < (NODE_DATA(nid)->node_start_pfn +
                         NODE_DATA(nid)->node_spanned_pages) )
                 {
 			THIS->__retvalue = nid;