leds: trigger: gpio: Convert to DEVICE_ATTR_RW()

Instead of custom wrapper, use DEVICE_ATTR_RW() directly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231103195310.948327-4-andriy.shevchenko@linux.intel.com


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