bus-util: convert bus_log_{parse,create}_error into defines

bus-util: convert bus_log_{parse,create}_error into defines

With SYSTEMD_LOG_LOCATION=1, it is much more useful to see the location
where the call to bus_log_{parse,create}_error() was made, rather then
the one-line body of the helper function. Also, it's our internal code,
so having a one-line non-inline function doesn't make much sense anyway.