should not call that if apic is disabled.

[ Impact: fix crash on certain UP configs ]
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
LKML-Reference: <4A09CCBB.2000306@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>