x86: pit_clockevent can be static

arch/x86/kernel/i8253.c:98:27: warning: symbol 'pit_clockevent' was not declared. Should it be static?

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>