iio: adc: rockchip_saradc: select IIO_TRIGGERED_BUFFER

The kernel fails to compile due to undefined reference to
devm_iio_triggered_buffer_setup() if IIO_TRIGGERED_BUFFER is not
enabled. The original patch [1] had this dependency. But somehow it
didn't make it into the kernel tree. Re-add it.

[1] https://lore.kernel.org/lkml/20200623233011.2319035-3-heiko@sntech.de/

Fixes: 4e130dc7 ("iio: adc: rockchip_saradc: Add support iio buffers")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/Kconfig

@@ -865,6 +865,8 @@ config ROCKCHIP_SARADC
 	tristate "Rockchip SARADC driver"
 	depends on ARCH_ROCKCHIP || (ARM && COMPILE_TEST)
 	depends on RESET_CONTROLLER
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
 	help
 	  Say yes here to build support for the SARADC found in SoCs from
 	  Rockchip.