ubik: Make udisk_Log* functions static

ubik: Make udisk_Log* functions static

Nothing uses the udisk_Log* functions outside of disk.c. Declare these
static to make sure they stay that way, to make it easier to change
their semantics.

Reviewed-on: https://gerrit.openafs.org/13069
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit f1d389e80367c7ea532441f9aa27a6cc3e2853a7)

Change-Id: I9c1cae678fc099f1eabe4aa6a661dcbc4ea72648
Reviewed-on: https://gerrit.openafs.org/13119
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>