amd-iommu: fix an off-by-one error in the AMD IOMMU driver.
The variable amd_iommu_last_bdf holds the maximum bdf of any device
controlled by an IOMMU, so the number of device entries needed is
amd_iommu_last_bdf+1. The function tbl_size used amd_iommu_last_bdf
instead. This would be a problem if the last device were a large
enough power of 2.