Adapt to the new term "core_id". While at it, fix the type and drop the
initialization to 0 (which is superfluous).

Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170913132417.24384-15-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>