irqchip/bcm2836: Make bcm2836_smp_boot_secondary static

The bcm2836_smp_boot_secondary() is not declared or used elsewhere
so make it static to fix the following warning:

drivers/irqchip/irq-bcm2836.c:227:12: warning: symbol 'bcm2836_smp_boot_secondary' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://lkml.kernel.org/r/1465407697-8116-1-git-send-email-ben.dooks@codethink.co.ukSigned-off-by: Jason Cooper <jason@lakedaemon.net>

drivers/irqchip/irq-bcm2836.c

@@ -224,8 +224,8 @@ static struct notifier_block bcm2836_arm_irqchip_cpu_notifier = {
 };
 
 #ifdef CONFIG_ARM
-int __init bcm2836_smp_boot_secondary(unsigned int cpu,
-				      struct task_struct *idle)
+static int __init bcm2836_smp_boot_secondary(unsigned int cpu,
+					     struct task_struct *idle)
 {
 	unsigned long secondary_startup_phys =
 		(unsigned long)virt_to_phys((void *)secondary_startup);