kcm: Remove unnecessary SLAB_PANIC for kmem_cache_create() in kcm_init

There has check NULL on kmem_cache_create on failure in kcm_init,
no need use SLAB_PANIC to panic the system.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>