gpio: use new gpio_set_config() helper in more places

As suggested by Linus Walleij, let's use the new gpio_set_config()
helper in gpiod_set_debounce() and gpiod_set_transitory().

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>