bos: Change to using char casts for ka functions

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.

Change-Id: I831ff0f8fbecec602d8c2b9112675938facfb06b
Reviewed-on: http://gerrit.openafs.org/7066
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>