irqchip: sun4i: Staticize sun4i_irq_ack()

sun4i_irq_ack() is only referenced in this file, so make it static.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: http://lkml.kernel.org/r/1373010070.14756.2.camel@phoenixSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/irqchip/irq-sun4i.c

@@ -38,7 +38,7 @@ static struct irq_domain *sun4i_irq_domain;
 
 static asmlinkage void __exception_irq_entry sun4i_handle_irq(struct pt_regs *regs);
 
-void sun4i_irq_ack(struct irq_data *irqd)
+static void sun4i_irq_ack(struct irq_data *irqd)
 {
 	unsigned int irq = irqd_to_hwirq(irqd);
 	unsigned int irq_off = irq % 32;