iommu/amd: Remove change_pte mmu_notifier call-back

All calls to this call-back are wrapped with
mmu_notifer_invalidate_range_start()/end(), making this
notifier pretty useless, so remove it.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Oded Gabbay <oded.gabbay@amd.com>