iommu: Fix off by one in dmar_get_fault_reason()

commit fefe1ed1 upstream.

fault_reason - 0x20 == ARRAY_SIZE(irq_remap_fault_reasons) is
one past the end of the array.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Cc: Youquan Song <youquan.song@intel.com>
Cc: walter harms <wharms@bfs.de>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/20120513170938.GA4280@elgon.mountainSigned-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: s/irq_remap_fault_reasons/intr_remap_fault_reasons/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iommu/dmar.c

@@ -1056,8 +1056,8 @@ static const char *intr_remap_fault_reasons[] =
 
 const char *dmar_get_fault_reason(u8 fault_reason, int *fault_type)
 {
-	if (fault_reason >= 0x20 && (fault_reason <= 0x20 +
-				     ARRAY_SIZE(intr_remap_fault_reasons))) {
+	if (fault_reason >= 0x20 && (fault_reason - 0x20 <
+					ARRAY_SIZE(intr_remap_fault_reasons))) {
 		*fault_type = INTR_REMAP;
 		return intr_remap_fault_reasons[fault_reason - 0x20];
 	} else if (fault_reason < ARRAY_SIZE(dma_remap_fault_reasons)) {