pinctrl: at91-pio4: irq argument as been removed from irq flow handlers

Irq argument as been removed from irq flow handlers so use the irq
descriptor to retrieve data we need.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>