gpiolib: remove gpio_set_debounce()

gpio_set_debounce() only has a single user, which is trivially
converted to gpiod_set_debounce().

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>