iio: adc: ad7768-1: Select GPIOLIB

iio: adc: ad7768-1: Select GPIOLIB

This driver provides a gpio chip a some related functions are not
stubbed if GPIOLIB is not built.

ad7768-1.c:420: undefined reference to `gpiochip_get_data'
ad7768-1.c:498: undefined reference to `devm_gpiochip_add_data_with_key'

Dual sign off reflects change of affiliation whilst this was under review.

Fixes: d569ae0f052e ("iio: adc: ad7768-1: Add GPIO controller support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512271235.WwAmAbOa-lkp@intel.com/
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Stable@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>