iio: adc: ti-adc081c: Select IIO_TRIGGERED_BUFFER to prevent build errors

Commit 08e05d1f ("ti-adc081c: Initial triggered buffer support") added
triggered buffer support but that also requires CONFIG_IIO_TRIGGERED_BUFFER,
otherwise we get errors from linker such as:

  drivers/built-in.o: In function `adc081c_remove':
  drivers/iio/adc/ti-adc081c.c:225: undefined reference to `iio_triggered_buffer_cleanup'

Fix these by explicitly selecting both CONFIG_IIO_TRIGGERED_BUFFER and
CONFIG_IIO_BUFFER in Kconfig for the driver.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/Kconfig

@@ -437,6 +437,8 @@ config STX104
 config TI_ADC081C
 	tristate "Texas Instruments ADC081C/ADC101C/ADC121C family"
 	depends on I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
 	help
 	  If you say yes here you get support for Texas Instruments ADC081C,
 	  ADC101C and ADC121C ADC chips.