ubik: calloc ubik_dbase

ubik: calloc ubik_dbase

Instead of using malloc and initializing various fields to 0, allocate
our ubik_dbase using calloc, to more easily ensure all fields are
initialized.

Change-Id: I5c2f345a82a2eb73d53ffc3e1b0fa408af6a8311
Reviewed-on: https://gerrit.openafs.org/13363
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>