iommu/vt-d: Fix a bug in intel_iommu_iova_to_phys() for huge page

intel_iommu_iova_to_phys() has a bug when it translates an IOVA for a huge
page onto its corresponding physical address. This commit fixes the bug by
accomodating the level of page entry for the IOVA and adds IOVA's lower
address to the physical address.

Cc: <stable@vger.kernel.org>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Yonghyun Hwang <yonghyun@google.com>
Fixes: 38717946 ("VT-d: Changes to support KVM")
Signed-off-by: Joerg Roedel <jroedel@suse.de>