Don't cast the return from calloc()

Don't cast the return from calloc()

calloc returns a (void *) argument. So we don't need to cast its
output before storing it.

Change-Id: Ibdfc61a8a2cf9779a0bfb17ff8ebf1f3bef3ea0e
Reviewed-on: http://gerrit.openafs.org/7456
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>