irqchip/metag-ext: Improve function-level documentation

Drop the variable irq which ceased to be a parameter.

Issue detected using Coccinelle (http://coccinelle.lip6.fr/)

Fixes: bd0b9ac4

 ("genirq: Remove irq argument from irq flow handlers").
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: James Hogan <james.hogan@imgtec.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kernel-janitors@vger.kernel.org
Cc: linux-metag@vger.kernel.org
Link: http://lkml.kernel.org/r/1475351192-27079-15-git-send-email-Julia.Lawall@lip6.fr


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>