iommu/amd: Free domain id when free a domain of struct dma_ops_domain

The current code missed freeing domain id when free a domain of
struct dma_ops_domain.

Signed-off-by: Baoquan He <bhe@redhat.com>
Fixes: ec487d1a ('x86, AMD IOMMU: add domain allocation and deallocation functions')
Signed-off-by: Joerg Roedel <jroedel@suse.de>