gpio: mxc: remove dead code after switch to DT-only

gpio: mxc: remove dead code after switch to DT-only

struct platform_device::id was only set by board code, but since i.MX
became a devicetree-only platform, this will always be -1
(PLATFORM_DEVID_NONE).

Note: of_alias_get_id() returns a negative number on error and base
treats all negative errors the same, so we need not add any additional
error handling.

Fixes: 0f2c7af45d7e ("gpio: mxc: Convert the driver to DT-only")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20250113-b4-imx-gpio-base-warning-v1-3-0a28731a5cf6@pengutronix.de
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>