sys: Don't cast returns from malloc()

sys: 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: I58b7695e3cf4b99f17869a46e1efca5c7daf6ff7
Reviewed-on: http://gerrit.openafs.org/7470
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>