backends/native: Fix double free of error

error is an autoptr, so must not be explicitly freed.

Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/1852
Fixes: 5c500ad402 ("backend: Move GPU ownership from the monitor manager to the backend")

https://gitlab.gnome.org/GNOME/mutter/merge_requests/960


(cherry picked from commit d70ddc65ea)

src/backends/native/meta-backend-native.c

@@ -583,7 +583,6 @@ on_udev_device_added (MetaUdev          *udev,
     {
       g_warning ("Failed to hotplug secondary gpu '%s': %s",
                  device_path, error->message);
-      g_error_free (error);
       return;
     }