irqchip: mxs: Fix function type for IRQCHIP_OF_DECLARE

Adding function type checking to IRQCHIP_OF_DECLARE found a type mismatch
with icoll_of_init. The function should return an error code or 0 on
success.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Jason Cooper <jason@lakedaemon.net>