ntp: fix 60-ntpd.list path

60-ntpd.list should be installed into the same path as ntp systemd service
file, like Fedora core; Orignal path refers
http://www.freedesktop.org/wiki/Software/systemd/timedated/

, but where
systemd_unitdir is assumed as /usr/lib/systemd, not /lib/systemd

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Joe MacDonald <joe@deserted.net>