Input: joystick - fix Kconfig warning for JOYSTICK_ADC

Input: joystick - fix Kconfig warning for JOYSTICK_ADC

Fix a Kconfig warning for JOYSTICK_ADC by also selecting
IIO_BUFFER.

WARNING: unmet direct dependencies detected for IIO_BUFFER_CB
  Depends on [n]: IIO [=y] && IIO_BUFFER [=n]
  Selected by [y]:
  - JOYSTICK_ADC [=y] && INPUT [=y] && INPUT_JOYSTICK [=y] && IIO [=y]

Fixes: 2c2b364fddd5 ("Input: joystick - add ADC attached joystick driver.")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20221104201238.31628-1-rdunlap@infradead.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>