(match value (%unset-value ...)) is equivalent here to
(match value (_ ...)). Even if you set 'log-file to some path, it's always
"syslog" in the configuration file.
* gnu/services/audio.scm (mpd): Fix buggy 'match'.
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Change-Id: If397919c2844d856c69fe00b8907b7b3fd86e564