pinctrl: ingenic: Mark probe function as __init

By using platform_driver_probe() instead of platform_driver_register(),
we can mark the ingenic_pinctrl_probe() function as __init.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>