GPIO controller might not be available when driver is being probed.
There are plenty of reasons why, one of which is deferred probe.

Since GPIOs are optional, return any error code we got to the upper
layer, including deferred probe. With that in mind, use dev_err_probe()
in order to avoid spamming the logs.

Fixes: 5a042273 ("drm/panel: Add ilitek ili9341 panel driver")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Link: https://lore.kernel.org/r/20240425142706.2440113-3-andriy.shevchenko@linux.intel.comSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240425142706.2440113-3-andriy.shevchenko@linux.intel.com