iommu/vt-d: Make sure copied over IR entries are not reused

Walk over the copied entries and mark the present ones as
allocated.

Tested-by: ZhenHua Li <zhen-hual@hp.com>
Tested-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>