drm/radeon: Fix pci_map_page() error checking

0 is a valid DMA address from pci_map_page(), use pci_dma_mapping_error()
instead to check for errors

[airlied: fix warning + two other places with errors.]

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/ati_pcigart.c b/drivers/gpu/drm/ati_pcigart.c
index 17be051..1c36492 100644
--- a/drivers/gpu/drm/ati_pcigart.c
+++ b/drivers/gpu/drm/ati_pcigart.c
@@ -152,7 +152,7 @@
 		/* we need to support large memory configurations */
 		entry->busaddr[i] = pci_map_page(dev->pdev, entry->pagelist[i],
 						 0, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-		if (entry->busaddr[i] == 0) {
+		if (pci_dma_mapping_error(dev->pdev, entry->busaddr[i])) {
 			DRM_ERROR("unable to map PCIGART pages!\n");
 			drm_ati_pcigart_cleanup(dev, gart_info);
 			address = NULL;