ACPI: Only count valid srat memory structures

Otherwise you could run into:
WARN_ON in numa_register_memblks(), because node_possible_map is zero

References: https://bugzilla.novell.com/show_bug.cgi?id=757888

On this machine (ProLiant ML570 G3) the SRAT table contains:
  - No processor affinities
  - One memory affinity structure (which is set disabled)

CC: Per Jessen <per@opensuse.org>
CC: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

arch/ia64/kernel/acpi.c

@@ -497,7 +497,7 @@ acpi_numa_processor_affinity_init(struct acpi_srat_cpu_affinity *pa)
 	srat_num_cpus++;
 }
 
-void __init
+int __init
 acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
 {
 	unsigned long paddr, size;
@@ -512,7 +512,7 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
 
 	/* Ignore disabled entries */
 	if (!(ma->flags & ACPI_SRAT_MEM_ENABLED))
-		return;
+		return -1;
 
 	/* record this node in proximity bitmap */
 	pxm_bit_set(pxm);
@@ -531,6 +531,7 @@ acpi_numa_memory_affinity_init(struct acpi_srat_mem_affinity *ma)
 	p->size = size;
 	p->nid = pxm;
 	num_node_memblks++;
+	return 0;
 }
 
 void __init acpi_numa_arch_fixup(void)