kauth: Fix some unnecessary variable assignments

Remove various places where a variable is assigned to, and then the
result never read.

Caught by clang-analyzer

Change-Id: Id8b7aeb6c54b7c93093ad44df5a9fe01575f2fbe
Reviewed-on: http://gerrit.openafs.org/9172
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>