afs: Refactor DoLockWarning

Change DoLockWarning around a little bit, so subsequent changes are
easier to follow. Move lastWarnTime/lastWarnPid so they are only
usable within this function.

This commit should incur no functional change.

Reviewed-on: http://gerrit.openafs.org/10794
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit c73883e7846fa0421cfac29830c27c9b6aacf5ed)

Change-Id: Ie419aa5110f9c72f99514c8159c10582747601db
Reviewed-on: http://gerrit.openafs.org/10837
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>