Linux CM: Use kernel allocator directly

Linux CM: Use kernel allocator directly

In another few locations within the Linux portion of the cache
manager, directly use the kernel allocator. We can do so here
because we can guarantee that the amount of memory being allocated
is less than the page size, and there is a kfree() in all of the
exit paths, so we don't need the magic freeing behaviour, either.

Change-Id: I9c9f3a0b8243b66cb081cd2b35f0d27aaa378934
Reviewed-on: http://gerrit.openafs.org/4752
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Derrick Brashear <shadow@dementia.org>