irqchip/mxs: Declare icoll_handle_irq() as static

After commit 5bb578a0c1b8 ("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 <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/irqchip/irq-mxs.c

···
 		 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;