BMP280 wrapper: Clean up floating point operations

src/platforms/posix/drivers/df_bmp280_wrapper/df_bmp280_wrapper.cpp

@@ -169,7 +169,7 @@ int DfBmp280Wrapper::_publish(struct baro_sensor_data &data)
 	// TODO: verify this, it's just copied from the MS5611 driver.
 
 	// Constant for now
-	const float MSL_PRESSURE = 101325.0f;
+	const double MSL_PRESSURE_KPA = 101325.0 / 1000.0;
 
 	/* tropospheric properties (0-11km) for standard atmosphere */
 	const double T1 = 15.0 + 273.15;	/* temperature at base height in Kelvin */
@@ -178,10 +178,10 @@ int DfBmp280Wrapper::_publish(struct baro_sensor_data &data)
 	const double R  = 287.05;	/* ideal gas constant in J/kg/K */
 
 	/* current pressure at MSL in kPa */
-	double p1 = MSL_PRESSURE / 1000.0f;
+	double p1 = MSL_PRESSURE_KPA;
 
 	/* measured pressure in kPa */
-	double p = data.pressure_pa / 1000.0f;
+	double p = static_cast<double>(data.pressure_pa) / 1000.0;
 
 	/*
 	 * Solve: