gpiolib: Remove duplicated function gpio_do_set_config()

gpio_set_config() simply call gpio_do_set_config(),
so remove the duplicated function.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20200116142927.58908-1-yuehaibing@huawei.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>