[PATCH] Input: touchscreen: fix kconfig dependency bug for TOUCHSCREEN_ADC

[Necip Fazil Yildiran]

When TOUCHSCREEN_ADC is enabled and IIO_BUFFER is disabled, it results
in the following Kbuild warning:

WARNING: unmet direct dependencies detected for IIO_BUFFER_CB
  Depends on [n]: IIO [=y] && IIO_BUFFER [=n]
  Selected by [y]:
  - TOUCHSCREEN_ADC [=y] && !UML && INPUT [=y] && INPUT_TOUCHSCREEN [=y] && IIO [=y]

The reason is that TOUCHSCREEN_ADC selects IIO_BUFFER_CB without depending
on or selecting IIO_BUFFER while IIO_BUFFER_CB depends on IIO_BUFFER. This
can also fail building the kernel.

Honor the kconfig dependency to remove unmet direct dependency warnings
and avoid any potential build failures.

Fixes: aa132ffb6b0a ("input: touchscreen: resistive-adc-touch: add generic resistive ADC touchscreen")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=209881
Signed-off-by: Necip Fazil Yildiran <fazilyildiran@xxxxxxxxx>
---
 drivers/input/touchscreen/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
index f012fe746df0..cc18f54ea887 100644
--- a/drivers/input/touchscreen/Kconfig
+++ b/drivers/input/touchscreen/Kconfig
@@ -96,6 +96,7 @@ config TOUCHSCREEN_AD7879_SPI
 config TOUCHSCREEN_ADC
 	tristate "Generic ADC based resistive touchscreen"
 	depends on IIO
+	select IIO_BUFFER
 	select IIO_BUFFER_CB
 	help
 	  Say Y here if you want to use the generic ADC
-- 
2.25.1