irqchip/mxs: Declare icoll_handle_irq() as static

After commit 5bb578a0 ("ARM: 9298/1: Drop custom mdesc->handle_irq()")
the function icoll_handle_irq() is only used within irq-mxs.c.  So declare
it as static to fix the warning about a missing prototype when building
with W=1.
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/irqchip/irq-mxs.c

@@ -130,7 +130,7 @@ static struct irq_chip asm9260_icoll_chip = {
 		 IRQCHIP_SKIP_SET_WAKE,
 };
 
-asmlinkage void __exception_irq_entry icoll_handle_irq(struct pt_regs *regs)
+static void __exception_irq_entry icoll_handle_irq(struct pt_regs *regs)
 {
 	u32 irqnr;