AMD IOMMU: __unmap_single: check for bad_dma_address instead of 0

Impact: minor fix

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 3133a0e..a7b6dec 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -983,7 +983,8 @@
 	dma_addr_t i, start;
 	unsigned int pages;
 
-	if ((dma_addr == 0) || (dma_addr + size > dma_dom->aperture_size))
+	if ((dma_addr == bad_dma_address) ||
+	    (dma_addr + size > dma_dom->aperture_size))
 		return;
 
 	pages = iommu_num_pages(dma_addr, size, PAGE_SIZE);