MIPS: ATH79: Set missing irq ack handler for ar7100-misc-intc irq chip

The irq ack handler was forgotten while introducing OF support.
Only ar71xx and ar933x based devices require it.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Acked-by: Alban Bedel <albeu@free.fr>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11163/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>