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: ec487d1a110a ('x86, AMD IOMMU: add domain allocation and deallocation functions')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 897940c..b5b117b 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1723,6 +1723,9 @@
 
 	free_pagetable(&dom->domain);
 
+	if (dom->domain.id)
+		domain_id_free(dom->domain.id);
+
 	kfree(dom);
 }