ubik: Save errno before logging

ubik: Save errno before logging

The value of errno can change after a syscall, and ViceLog may issue
syscalls (such as write()). So, make sure we save errno here before
calling ViceLog().

Issue spotted by kaduk@mit.edu.

Reviewed-on: https://gerrit.openafs.org/13263
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 9ff5f8f7601cc9761cc6a4ef0e8b7c8c2c8dddb5)

Change-Id: I4f41ca758574e0d58659788467372af71a5f75f2
Reviewed-on: https://gerrit.openafs.org/13898
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>