drm/nouveau/gem: fix object reference leak in a failure path

Reported-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -342,6 +342,7 @@ retry:
 		if (nvbo->reserved_by && nvbo->reserved_by == file_priv) {
 			NV_ERROR(dev, "multiple instances of buffer %d on "
 				      "validation list\n", b->handle);
+			drm_gem_object_unreference_unlocked(gem);
 			validate_fini(op, NULL);
 			return -EINVAL;
 		}