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/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index a64811a..4f7a170 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -347,7 +347,8 @@
 		return -ENOMEM;
 	rdev->dummy_page.addr = pci_map_page(rdev->pdev, rdev->dummy_page.page,
 					0, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-	if (!rdev->dummy_page.addr) {
+	if (pci_dma_mapping_error(rdev->pdev, rdev->dummy_page.addr)) {
+		dev_err(&rdev->pdev->dev, "Failed to DMA MAP the dummy page\n");
 		__free_page(rdev->dummy_page.page);
 		rdev->dummy_page.page = NULL;
 		return -ENOMEM;