iio: adc: bd79124: Add GPIOLIB dependency

iio: adc: bd79124: Add GPIOLIB dependency

The bd79124 has ADC inputs which can be muxed to be GPIOs. The driver
supports this by registering a GPIO-chip for channels which aren't used
as ADC.

The Kconfig entry does not handle the dependency to GPIOLIB, which
causes errors:

ERROR: modpost: "devm_gpiochip_add_data_with_key" [drivers/iio/adc/rohm-bd79124.ko] undefined!
ERROR: modpost: "gpiochip_get_data" [drivers/iio/adc/rohm-bd79124.ko] undefined!

at linking phase if GPIOLIB is not configured to be used.

Fix this by adding dependency to the GPIOLIB.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202508131533.5sSkq80B-lkp@intel.com/
Fixes: 3f57a3b9ab74 ("iio: adc: Support ROHM BD79124 ADC")
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://patch.msgid.link/6837249bddf358924e67566293944506206d2d62.1755076369.git.mazziesaccount@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>