drm/qxl: Do not leak memory if qxl_release_list_add fails

commit 8451cc96 upstream.

If the function fails reference counter to the object is not decremented
causing leaks.
This is hard to spot as it happens only on very low memory situations.
Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/gpu/drm/qxl/qxl_ioctl.c

@@ -122,8 +122,10 @@ static struct qxl_bo *qxlhw_handle_to_bo(struct qxl_device *qdev,
 	qobj = gem_to_qxl_bo(gobj);
 
 	ret = qxl_release_list_add(release, qobj);
-	if (ret)
+	if (ret) {
+		drm_gem_object_unreference_unlocked(gobj);
 		return NULL;
+	}
 
 	return qobj;
 }