libafs: initialize hard mount last errors

Initialize the values of the server last errors
introduced in commit 94a8ce970d57498583e249ea61725fce1ee53a50
to avoid logging garbage for the last error codes.

Reviewed-on: http://gerrit.openafs.org/10082
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 495d6fcbba1630b136d9c1b4256f0a71666a8a7b)

Change-Id: I4402838d761ab4bbb3e0798f219dfb825347b090
Reviewed-on: http://gerrit.openafs.org/10085
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>