gpio: omap: Remove unneeded include

The <linux/irqchip/chained_irq.h> header is already included
when selecting GPIOLIB_IRQCHIP so there is no need to do it
in the driver. This is a left over from commit fb655f57
("gpio: omap: convert driver to use gpiolib irqchip").

Signed-off-by: Javier Martinez Canillas <jmartinez@softcrates.net>
Acked-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>