irqchip/vic: Improve function-level documentation

The associated function, vic_init_cascaded, has never had a variable
irq_start.

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

)

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kernel-janitors@vger.kernel.org
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1475351192-27079-14-git-send-email-Julia.Lawall@lip6.fr


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