AP_BattMonitor: set default I2C bus for Solo and Maxell drivers

libraries/AP_BattMonitor/AP_BattMonitor.cpp

@@ -114,11 +114,13 @@ AP_BattMonitor::init()
                 break;
 #if HAL_BATTMON_SMBUS_ENABLE
             case AP_BattMonitor_Params::BattMonitor_TYPE_SOLO:
+                _params[instance]._i2c_bus.set_default(AP_BATTMONITOR_SMBUS_BUS_INTERNAL);
                 drivers[instance] = new AP_BattMonitor_SMBus_Solo(*this, state[instance], _params[instance],
                                                                   hal.i2c_mgr->get_device(_params[instance]._i2c_bus, AP_BATTMONITOR_SMBUS_I2C_ADDR,
                                                                                           100000, true, 20));
                 break;
             case AP_BattMonitor_Params::BattMonitor_TYPE_MAXELL:
+                _params[instance]._i2c_bus.set_default(AP_BATTMONITOR_SMBUS_BUS_EXTERNAL);
                 drivers[instance] = new AP_BattMonitor_SMBus_Maxell(*this, state[instance], _params[instance],
                                                                     hal.i2c_mgr->get_device(_params[instance]._i2c_bus, AP_BATTMONITOR_SMBUS_I2C_ADDR,
                                                                                             100000, true, 20));