ptserver: Don't ignore ubik_Write failures

If we can't write to the ubik database, then that's a bad thing.
Don't ignore it.

Caught by clang-analyzer

Change-Id: I08b57a74405cc563c6141251fd3d433b2904ea0e
Reviewed-on: http://gerrit.openafs.org/9176
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>