x86, mm: Use max_low_pfn for ZONE_NORMAL on 64-bit

64-bit has no highmem so max_low_pfn is always the same as
'max_pfn'.

Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/1320155902-10424-5-git-send-email-penberg@kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/init_64.c

@@ -623,7 +623,7 @@ static void __init zone_sizes_init(void)
 #ifdef CONFIG_ZONE_DMA32
 	max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN;
 #endif
-	max_zone_pfns[ZONE_NORMAL] = max_pfn;
+	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
 
 	free_area_init_nodes(max_zone_pfns);
 }