irqchip: keystone: Remove warning unsigned 'kirq->irq' is never less than zero

Remove static checker warning:

	drivers/irqchip/irq-keystone.c:166 keystone_irq_probe()
	warn: unsigned 'kirq->irq' is never less than zero.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Link: https://lkml.kernel.org/r/1409246189-29727-1-git-send-email-grygorii.strashko@ti.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>