x86: Fix a couple of sparse warnings in arch/x86/kernel/apic/io_apic.c

Impact: cleanup

This patch fixes the following sparse warnings:

 arch/x86/kernel/apic/io_apic.c:3602:17: warning: symbol 'hpet_msi_type'
 was not declared. Should it be static?

 arch/x86/kernel/apic/io_apic.c:3467:30: warning: Using plain integer as
 NULL pointer

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.com>
LKML-Reference: <1237741871-5827-2-git-send-email-dmitri.vorobiev@movial.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>