tunefs: Don't combine GEOM journaling with SU

GEOM journaling shouldn't be used at the same time as soft updates, so
don't enable one if the other is already in use.

MFC after: 1 week
PR: 293896
Reviewed by: mckusick
Differential Revision: https://reviews.freebsd.org/D56002

(cherry picked from commit b1f72dd2a9a5e69a310b9e76b55f16cff433b8da)