IB/ehca: use kvfree() in ipz_queue_{cd}tor()

Use kvfree() instead of open-coding it.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
Cc: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Cc: Christoph Raisch <raisch@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>