Init ADC keypad analog input (#14585)

Marlin/src/module/temperature.cpp

@@ -1675,6 +1675,9 @@ void Temperature::init() {
   #if ENABLED(FILAMENT_WIDTH_SENSOR)
     HAL_ANALOG_SELECT(FILWIDTH_PIN);
   #endif
+  #if HAS_ADC_BUTTONS
+    HAL_ANALOG_SELECT(ADC_KEYPAD_PIN);
+  #endif
 
   HAL_timer_start(TEMP_TIMER_NUM, TEMP_TIMER_FREQUENCY);
   ENABLE_TEMPERATURE_INTERRUPT();