systemctl: more cleanup

This is followup on 05cae7f3431446236139434ee58a6275f3cb31e8

I think the intention was to use the newly introduced 'path'
variable in the inner loop instead of p.
udev: avoid use of uninitialized err

After 1ea972174baba40dbc80c51cbfc4edc49764b59b err is no longer
set unless we hit a special case. Initialize it to 0 and remove
a check that will never fail.