amd_iommu: fix nasty bug that caused ILLEGAL_DEVICE_TABLE_ENTRY errors

We are on 64-bit so better use u64 instead of u32 to deal with
addresses:

static void __init iommu_set_device_table(struct amd_iommu *iommu)
{
        u64 entry;
  ...
        entry = virt_to_phys(amd_iommu_dev_table);
  ...

(I am wondering why gcc 4.2.x did not warn about the assignment
between u32 and unsigned long.)

Cc: iommu@lists.linux-foundation.org
Cc: stable@kernel.org
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>