util: Don't cast returns from malloc()

util: Don't cast returns from malloc()

malloc() returns a (void *) on all of our current platforms. So,
don't bother casting the return value before assigning it - it is
unnecessary noise.

Change-Id: I8287709413fe0e34f417936d1fc64c421fea6d28
Reviewed-on: http://gerrit.openafs.org/7472
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>