gpio: pxa: remove gpio_to_irq() from hw irq handlers

gpio_to_irq() API expected to be used by GPIO consumers and
not drivers and there are no guarantee that its gpiolib implementation
is irq safe.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>