gpio: shared: extend the ifdef guard to gpio_shared_find_entry()

gpio: shared: extend the ifdef guard to gpio_shared_find_entry()

While this function is supposed to be used by all scanning functions, so
far we only have a single one for OF trees. Once we add support for ACPI
and software nodes, we'll drop the CONFIG_OF guard around this routine
but in order to avoid build warnings, let's extend it to cover it in the
meantime.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511180232.EItKeYjY-lkp@intel.com/
Link: https://lore.kernel.org/r/20251118-gpiolib-shared-of-guard-v1-1-e4ef149a2e0b@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>