Fix for tunefs(8) unable to add a UFS/FFS soft update journal.

The reported bug is UFS: bad file descriptor: soft update journaling
can not be enabled on some FreeBSD-provided disk images – failed
to write updated cg.

The UFS library (libufs(3)) failed to reopen its disk descriptor
when first attempting to update a cylinder group. The error only
occurred when trying to add journaling to a filesystem whose first
cylinder group was too full to hold the journal.

PR: 259090
MFC after: 1 week
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 5c7ba6bdf83fda82cce70f384e2ec8218f13002e)