x86/mm/init.c: Fix devmem_is_allowed() off by one

Fixing an off-by-one error in devmem_is_allowed(), which allows
accesses to physical addresses 0x100000-0x100fff, an extra page
past 1MB.

Signed-off-by: T Makphaibulchoke <tmac@hp.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: yinghai@kernel.org
Cc: tiwai@suse.de
Cc: dhowells@redhat.com
Link: http://lkml.kernel.org/r/1346210503-14276-1-git-send-email-tmac@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/init.c

@@ -319,7 +319,7 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
  */
 int devmem_is_allowed(unsigned long pagenr)
 {
-	if (pagenr <= 256)
+	if (pagenr < 256)
 		return 1;
 	if (iomem_is_exclusive(pagenr << PAGE_SHIFT))
 		return 0;