kmix assumes volume range 1:100 for oss mixer instead of 0:100.

Summary:
See https://bugs.kde.org/344468
and https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=184996

Reviewers: #freebsd, marten, adridg, ltoscano

Reviewed By: #freebsd, adridg

Subscribers: adridg, ltoscano, rakuco

Differential Revision: https://phabricator.kde.org/D6925