iommu/amd: Handle large pages correctly in free_pagetable

commit 0b3fff54 upstream.

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

Fixes: 5c34c403 ("iommu/amd: Fix memory leak in free_pagetable")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>