iommu: Fix off by one in dmar_get_fault_reason()

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>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/20120513170938.GA4280@elgon.mountain


Signed-off-by: Ingo Molnar <mingo@kernel.org>