meson-installed polkit fails to run with default usr/lib prefix

With default /usr/lib prefix set by meson, polkit service would fail
with sigsegv. Changing prefix to /usr fixed the issue.
Also /usr/lib conforms FHS more than /usr/local/lib in terms
of a system service.
1 job for meson-prefix-usr in 2 minutes and 5 seconds (queued for 3 seconds)
Status Job ID Name Coverage
passed #5631600