drm/nv50-/fb: use dma_mapping_error() to check dma_map_page() result

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/fb/nv50.c

@@ -253,8 +253,8 @@ nv50_fb_ctor(struct nouveau_object *parent, struct nouveau_object *engine,
 		priv->r100c08 = dma_map_page(nv_device_base(device),
 					     priv->r100c08_page, 0, PAGE_SIZE,
 					     DMA_BIDIRECTIONAL);
-		if (!priv->r100c08)
-			nv_warn(priv, "failed 0x100c08 page map\n");
+		if (dma_mapping_error(nv_device_base(device), priv->r100c08))
+			return -EFAULT;
 	} else {
 		nv_warn(priv, "failed 0x100c08 page alloc\n");
 	}

drivers/gpu/drm/nouveau/core/subdev/fb/nvc0.c

@@ -97,7 +97,7 @@ nvc0_fb_ctor(struct nouveau_object *parent, struct nouveau_object *engine,
 		priv->r100c10 = dma_map_page(nv_device_base(device),
 					     priv->r100c10_page, 0, PAGE_SIZE,
 					     DMA_BIDIRECTIONAL);
-		if (!priv->r100c10)
+		if (dma_mapping_error(nv_device_base(device), priv->r100c10))
 			return -EFAULT;
 	}