intel-iommu: Fix array overflow

Fix possible array overflow:

drivers/pci/intel-iommu.c: In function ¡dmar_get_fault_reason¢:
drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds
drivers/pci/intel-iommu.c: In function ¡iommu_page_fault¢:
drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: Mark Gross <mgross@linux.intel.com>
Acked-by: "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pci/intel-iommu.c

@@ -749,8 +749,8 @@ static char *fault_reason_strings[] =
 
 char *dmar_get_fault_reason(u8 fault_reason)
 {
-	if (fault_reason > MAX_FAULT_REASON_IDX)
-		return fault_reason_strings[MAX_FAULT_REASON_IDX];
+	if (fault_reason >= MAX_FAULT_REASON_IDX)
+		return fault_reason_strings[MAX_FAULT_REASON_IDX - 1];
 	else
 		return fault_reason_strings[fault_reason];
 }