llvm: Fixed remaining warnings for llvm

This commit addresses warnings emitted from the llvm
compilers which were not encountered with gnu.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/t6713/t6713.hpp

@@ -141,7 +141,6 @@ class T6713 : public ICO2Sensor {
 	uint16_t getSensorData (t6713_co2::MODBUS_COMMANDS cmd);
         t6713_co2::STATUS getStatus();
 
-        int bus;
         mraa::I2c* i2c;
         mraa::Result status;
 };