irqchip/jcore-aic: Fix non static symbol warning

Fixes the following sparse warning:

drivers/irqchip/irq-jcore-aic.c:47:12: warning:
 symbol 'aic_irq_of_init' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Link: https://lkml.kernel.org/r/1471706788-27587-1-git-send-email-weiyj.lk@gmail.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>