gpio: 74x164: Use module_spi_driver boiler plate function

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Florian Fainelli <florian@openwrt.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>