iio: adc: ad7780: Add missing GPIOLIB dependency

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/adc/Kconfig

@@ -145,6 +145,7 @@ config AD7887
 config AD7780
 	tristate "Analog Devices AD7780 AD7781 ADC driver"
 	depends on SPI
+	depends on GPIOLIB
 	help
 	  Say yes here to build support for Analog Devices
 	  AD7780 and AD7781 SPI analog to digital convertors (ADC).