drm/panel: himax-hx8394: switch to devm_gpiod_get_optional() for reset_gpio

Switch the driver to use devm_gpiod_get_optional() on reset_gpio to avoid
driver probe issues when reset line is not specified.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240701085837.50855-3-manikandan.m@microchip.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240701085837.50855-3-manikandan.m@microchip.com