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/hisilicon/kirin/kirin_drm_drv.c

@@ -207,8 +207,8 @@ static int kirin_drm_bind(struct device *dev)
 	int ret;
 
 	drm_dev = drm_dev_alloc(driver, dev);
-	if (!drm_dev)
-		return -ENOMEM;
+	if (IS_ERR(drm_dev))
+		return PTR_ERR(drm_dev);
 
 	drm_dev->platformdev = to_platform_device(dev);