drm: Distinguish no name from ENOMEM in set_unique()

If passing name == NULL to drm_drv_set_unique() we now get -ENOMEM
as kstrdup() returns NULL. Instead check for this explicitly and
return -EINVAL if no name is provided.
Signed-off-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20160921145919.13754-1-teg@jklm.no

drivers/gpu/drm/drm_drv.c

@@ -338,6 +338,9 @@ void drm_minor_release(struct drm_minor *minor)
 
 static int drm_dev_set_unique(struct drm_device *dev, const char *name)
 {
+	if (!name)
+		return -EINVAL;
+
 	kfree(dev->unique);
 	dev->unique = kstrdup(name, GFP_KERNEL);