spapr: get numa node mapping from possible_cpus instead of numa_get_node_for_cpu()

it's safe to remove thread node_id != core node_id error
branch as machine_set_cpu_numa_node() also does mismatch
check and is called even before any CPU is created.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <1494415802-227633-10-git-send-email-imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
