bos: Change to using char casts for ka functions

The ka_IsZero and ka_PrintBytes function just use char strings. Cast
directly, rather than going via a helper functions to simplify this
code.

The helper functions add complexity, and additional dependencies which
cause problems with some uses of this code.

Reviewed-on: http://gerrit.openafs.org/7066
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 46c5aabfc6f5af2875e8b20252a17955ad89dd38)

Change-Id: Ifee3178e5cdc2eab947f759541864ecea4345b7a
Reviewed-on: http://gerrit.openafs.org/10867
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>