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
diff --git a/drivers/gpu/drm/vc4/vc4_drv.c b/drivers/gpu/drm/vc4/vc4_drv.c
index deec535..3c9e7f6 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.c
+++ b/drivers/gpu/drm/vc4/vc4_drv.c
@@ -233,8 +233,8 @@
 		return -ENOMEM;
 
 	drm = drm_dev_alloc(&vc4_drm_driver, dev);
-	if (!drm)
-		return -ENOMEM;
+	if (IS_ERR(drm))
+		return PTR_ERR(drm);
 	platform_set_drvdata(pdev, drm);
 	vc4->dev = drm;
 	drm->dev_private = vc4;