[PATCH] ia64: fix is_headless_node() for SN

Without this patch, SN machines which have nodes that contain memory only (no
CPUs will hang.

include/asm-ia64/sn/nodepda.h

@@ -128,7 +128,7 @@ typedef struct irqpda_s irqpda_t;
  * Check if given a compact node id the corresponding node has all the
  * cpus disabled. 
  */
-#define is_headless_node(cnode)		(!node_to_cpu_mask[cnode])
+#define is_headless_node(cnode)		(nr_cpus_node(cnode) == 0)
 
 /*
  * Check if given a node vertex handle the corresponding node has all the