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>
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 3ad510b..4f2a762 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -96,7 +96,7 @@
 void acpi_numa_slit_init (struct acpi_table_slit *slit);
 void acpi_numa_processor_affinity_init (struct acpi_srat_cpu_affinity *pa);
 void acpi_numa_x2apic_affinity_init(struct acpi_srat_x2apic_cpu_affinity *pa);
-void acpi_numa_memory_affinity_init (struct acpi_srat_mem_affinity *ma);
+int acpi_numa_memory_affinity_init (struct acpi_srat_mem_affinity *ma);
 void acpi_numa_arch_fixup(void);
 
 #ifdef CONFIG_ACPI_HOTPLUG_CPU