gpio: pcf857x: Remove pdata argument to pcf857x_irq_domain_init()

The argument is not used, remove it. No board registers a pcf857x device
with an IRQ without specifying platform data, IRQ domain registration
behaviour is thus not affected by this change.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>