drm/panel: ltk050h3146w: only print message when GPIO getting is not EPROBE_DEFER

devm_gpiod_get_optional may return EPROBE_DEFER in case the GPIO
controller isn't yet probed when the panel driver is being probed.

In that case, a spurious and confusing error message about not being
able to get the reset GPIO is printed even though later on the device
actually manages to get probed.

Use dev_err_probe instead so that the message is only printed when it
truly matters.

Cc: Quentin Schulz <foss+kernel@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240104-ltk-dev_err_probe-v1-1-8ef3c0b585d8@theobroma-systems.com