x86/vt-d: Fix comment for dma_pte_free_pagetable()

dma_pte_free_pagetable no longer depends on last level ptes
being clear, it clears them itself.  Fix up the comment to
match.

Cc: Jiang Liu <jiang.liu@linux.intel.com>
Suggested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -1143,7 +1143,7 @@ next:
 	} while (!first_pte_in_page(++pte) && pfn <= last_pfn);
 }
 
-/* free page table pages. last level pte should already be cleared */
+/* clear last level (leaf) ptes and free page table pages. */
 static void dma_pte_free_pagetable(struct dmar_domain *domain,
 				   unsigned long start_pfn,
 				   unsigned long last_pfn)