Use the return value of ppc_set_compat_all() to check failures,
which is preferred over hijacking local_err.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20200914123505.612812-7-groug@kaod.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>