AP_HAL_Linux: add semaphore to AnalogIn::channel to make it thread safe

libraries/AP_HAL_Linux/AnalogIn_ADS1115.cpp

@@ -49,6 +49,7 @@ AnalogIn_ADS1115::AnalogIn_ADS1115()
 
 AP_HAL::AnalogSource* AnalogIn_ADS1115::channel(int16_t pin)
 {
+    WITH_SEMAPHORE(_semaphore);
     for (uint8_t j = 0; j < _channels_number; j++) {
         if (_channels[j] == nullptr) {
             _channels[j] = new AnalogSource_ADS1115(pin);

libraries/AP_HAL_Linux/AnalogIn_ADS1115.h

@@ -37,4 +37,5 @@ private:
     AP_ADC_ADS1115 *_adc;
     AnalogSource_ADS1115 *_channels[ADS1115_ADC_MAX_CHANNELS];
     uint32_t _last_update_timestamp;
+    HAL_Semaphore _semaphore;
 };

libraries/AP_HAL_Linux/AnalogIn_Navio2.cpp

@@ -107,6 +107,7 @@ float AnalogIn_Navio2::servorail_voltage(void)
 
 AP_HAL::AnalogSource *AnalogIn_Navio2::channel(int16_t pin)
 {
+    WITH_SEMAPHORE(_semaphore);
     for (uint8_t j = 0; j < _channels_number; j++) {
         if (_channels[j] == nullptr) {
             _channels[j] = new AnalogSource_Navio2(pin);

libraries/AP_HAL_Linux/AnalogIn_Navio2.h

@@ -36,4 +36,5 @@ private:
     uint8_t _channels_number = NAVIO_ADC_MAX_CHANNELS;
     AP_HAL::AnalogSource *_board_voltage_pin = nullptr;
     AP_HAL::AnalogSource *_servorail_pin = nullptr;
+    HAL_Semaphore _semaphore;
 };