irqchip/brcmstb-l2: Make of probe function static

The probe functions in this driver is not exported or declared
so make it static to fix the following warning:

drivers/irqchip/irq-brcmstb-l2.c:115:12: warning: symbol 'brcmstb_l2_intc_of_init' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://lkml.kernel.org/r/1465408940-16414-1-git-send-email-ben.dooks@codethink.co.uk


Signed-off-by: Jason Cooper <jason@lakedaemon.net>