iommu/amd: Handle large pages correctly in free_pagetable

[ Upstream commit 0b3fff54bc01e8e6064d222a33e6fa7adabd94cd ]

Make sure that we are skipping over large PTEs while walking
the page-table tree.

Cc: stable@kernel.org
Fixes: 5c34c403 ("iommu/amd: Fix memory leak in free_pagetable")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>