apt: fix libdir path for apt.systemd.daily

apt: fix libdir path for apt.systemd.daily

It should be ${libdir} rather than /usr/lib, otherwise it would fail
when multilib:

MACHINE = "qemux86-64"
require conf/multilib.conf
MULTILIBS = "multilib:lib32"
DEFAULTTUNE_virtclass-multilib-lib32 = "x86"

$ bitbake apt
[snip]
install: target /path/to/apt/1.2.12-r0/image/usr/lib/apt is not a directory: No such file or directory
[snip]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>