butc: Initialize RPC outputs at top of function

butc: Initialize RPC outputs at top of function

RPC handlers are a little bit special in that their output parameters
are discarded on error and an Rx abort is sent instead of the usual
response fields.  Nonetheless, it is good code hygeine to adhere to
the practices we use for the rest of the functions in the tree:
initialize output variables before the first return.

Change-Id: I6c2e25b04ccb6277bd28e398121723b92fe42b04
Reviewed-on: https://gerrit.openafs.org/13314
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>