gpio: pcf857x: change to devm_request_threaded_irq

Remove the request_irq and use devm_request_threaded_irq
also cleanup free_irq. devm_* takes care of that.

Signed-off-by: George Cherian <george.cherian@ti.com>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>