kmem_cache_destroy() can handle NULL pointer correctly, so there is no
need to check NULL pointer before calling kmem_cache_destroy()
Signed-off-by: Chengguang Xu <cgxu519@gmx.com> Acked-by: Johannes Thumshirn <jth@kernel.org> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>