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>

drivers/irqchip/irq-keystone.c

@@ -36,7 +36,7 @@ struct keystone_irq_device {
 	struct device		*dev;
 	struct irq_chip		 chip;
 	u32			 mask;
-	u32			 irq;
+	int			 irq;
 	struct irq_domain	*irqd;
 	struct regmap		*devctrl_regs;
 	u32			devctrl_offset;