irq: versatile: delete dangling variable

This one was just creating noise like this:

drivers/irqchip/irq-versatile-fpga.c: In function 'fpga_irq_of_init':
drivers/irqchip/irq-versatile-fpga.c:180:24: warning: unused variable 'f'
Reported-by: NRussell King <linux@arm.linux.org.uk>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NOlof Johansson <olof@lixom.net>

drivers/irqchip/irq-versatile-fpga.c

@@ -177,7 +177,6 @@ void __init fpga_irq_init(void __iomem *base, const char *name, int irq_start,
 int __init fpga_irq_of_init(struct device_node *node,
 			    struct device_node *parent)
 {
-	struct fpga_irq_data *f;
 	void __iomem *base;
 	u32 clear_mask;
 	u32 valid_mask;