gpio: pcf857x: use client->irq for gpio_to_irq()

6e20a0a429bd4dc07d6de16d9c247270e04e4aa0
(gpio: pcf857x: enable gpio_to_irq() support)
added gpio_to_irq() support on pcf857x driver,
but it used pdata->irq.
This patch modifies driver to use client->irq instead of it.
It modifies kzm9g board platform settings,
and device probe information too.
This patch is tested on kzm9g board

Reported-by: Christian Engelmayer <christian.engelmayer@frequentis.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>