x86/time: Make setup_default_timer_irq() static

This function isn't used outside of time.c, so let's mark it static.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1497321029-29049-1-git-send-email-douly.fnst@cn.fujitsu.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>