leds: trigger: gpio: Convert to use kstrtox()

sscanf() is a heavy one and moreover requires additional boundary checks.
Convert driver to use kstrtou8() in gpio_trig_inverted_store().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231103195310.948327-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Lee Jones <lee@kernel.org>