krb5_wrap: Remove extra parentheses causing compile error

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Thu Sep  1 21:02:54 CEST 2016 on sn-devel-144
