bos_util: Fix buffer overflow

Get rid of a buffer overflow in the bos_util utility, by just
printing the key from the 'tbuffer' string, rather than copying
it into 'x' which is too small for it.

Change-Id: Ia364fb63edb9e40a887e77aad833689a99b4ea7c
Reviewed-on: http://gerrit.openafs.org/9291
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>