gpio: davinci: fix check for unbanked gpio

This patch fixes a check for offset in gpio_to_irq_unbanked()
and also assigns gpio_irq, gpio_unbanked of chips[0] to
appropriate values which is used in gpio_to_irq_unbanked()
function.

Without this patch, unbanked IRQ handling is broken.

Reported-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>