gpio: tn48m: enable building the module with COMPILE_TEST=y

Extend the build coverage by allowing to build the module with
COMPILE_TEST enabled.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250408-gpio-compile-test-v1-6-140e108e9392@linaro.org


Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>