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/msm/msm_drv.c

@@ -347,9 +347,9 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
 	int ret;
 
 	ddev = drm_dev_alloc(drv, dev);
-	if (!ddev) {
+	if (IS_ERR(ddev)) {
 		dev_err(dev, "failed to allocate drm_device\n");
-		return -ENOMEM;
+		return PTR_ERR(ddev);
 	}
 
 	platform_set_drvdata(pdev, ddev);