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/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index f0851db..cc45d98 100644
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -86,8 +86,8 @@
 	int r;
 
 	dev = drm_dev_alloc(&driver, &interface->dev);
-	if (!dev)
-		return -ENOMEM;
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
 
 	r = drm_dev_register(dev, (unsigned long)udev);
 	if (r)