leds: trigger: gpio: GPIO 0 is valid

Allow all valid GPIOs to be used in the driver.

Fixes: 17354bfe ("leds: Add gpio-led trigger")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>