systemd-journal: if prefix is set, do not set prefixed key as link to the original one,

but set the key as original not linked to the original.

Signed-off-by: Juhász Viktor <viktor.juhasz@balabit.com>
Merge pull request #238 from juhaszviktor/3.6/f/journald-source

systemd-journal: if prefix is set, do not set prefixed key as link to th...