drm: Don't swallow error codes in drm_dev_alloc()

There are many reasons other than ENOMEM that drm_dev_init() can
fail. Return ERR_PTR rather than NULL to be able to distinguish
these in the caller.

Signed-off-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20160921145919.13754-2-teg@jklm.no

drivers/gpu/drm/arc/arcpgu_drv.c

@@ -198,8 +198,8 @@ static int arcpgu_probe(struct platform_device *pdev)
 	int ret;
 
 	drm = drm_dev_alloc(&arcpgu_drm_driver, &pdev->dev);
-	if (!drm)
-		return -ENOMEM;
+	if (IS_ERR(drm))
+		return PTR_ERR(drm);
 
 	ret = arcpgu_load(drm);
 	if (ret)