x86/amd-iommu: Use fetch_pte in iommu_unmap_page

Instead of reimplementing existing logic use fetch_pte to
walk the page table in iommu_unmap_page.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 29bcd35..5e52798 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -546,23 +546,10 @@
 static void iommu_unmap_page(struct protection_domain *dom,
 			     unsigned long bus_addr)
 {
-	u64 *pte;
+	u64 *pte = fetch_pte(dom, bus_addr);
 
-	pte = &dom->pt_root[IOMMU_PTE_L2_INDEX(bus_addr)];
-
-	if (!IOMMU_PTE_PRESENT(*pte))
-		return;
-
-	pte = IOMMU_PTE_PAGE(*pte);
-	pte = &pte[IOMMU_PTE_L1_INDEX(bus_addr)];
-
-	if (!IOMMU_PTE_PRESENT(*pte))
-		return;
-
-	pte = IOMMU_PTE_PAGE(*pte);
-	pte = &pte[IOMMU_PTE_L1_INDEX(bus_addr)];
-
-	*pte = 0;
+	if (pte)
+		*pte = 0;
 }
 
 /*