Use calloc, rather than malloc/memset

Use calloc, rather than malloc/memset

Rather than doing
	a = malloc(sizeof(me));
	memset(a, 0, sizeof(me));

Just use
        a = calloc(1, sizeof(me));

This is simpler, shorter, and removes the potential for the size of
the memset not matching the size of the malloc (or the target of the
memset being wrong!)

Where the size is of the form (n * sizeof(me)), we also use
calloc(n, sizeof(me));

Change-Id: Ia0f75665c1031fd2982eee0e1d8c8ebe23d7fbc0
Reviewed-on: http://gerrit.openafs.org/7454
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>