DF wrappers: use abs time instead of DF timestamp

The timestamp in the DriverFramework is not the same as the one
provided by hrt_absolute_time() in PX4. Because we are publishing on the
PX4 side, let's also use the timestamp from there.

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

@@ -161,7 +161,7 @@ int DfBmp280Wrapper::_publish(struct baro_sensor_data &data)
 	perf_begin(_baro_sample_perf);
 
 	baro_report baro_report = {};
-	baro_report.timestamp = data.last_read_time_usec;
+	baro_report.timestamp = hrt_absolute_time();
 
 	baro_report.pressure = data.pressure_pa;
 	baro_report.temperature = data.temperature_c;

src/platforms/posix/drivers/df_hmc5883_wrapper/df_hmc5883_wrapper.cpp

@@ -275,7 +275,7 @@ int DfHmc9250Wrapper::_publish(struct mag_sensor_data &data)
 	perf_begin(_mag_sample_perf);
 
 	mag_report mag_report = {};
-	mag_report.timestamp = data.last_read_time_usec;
+	mag_report.timestamp = hrt_absolute_time();
 
 	/* The standard external mag by 3DR has x pointing to the
 	 * right, y pointing backwards, and z down, therefore switch x

src/platforms/posix/drivers/df_mpu9250_wrapper/df_mpu9250_wrapper.cpp

@@ -408,7 +408,7 @@ int DfMpu9250Wrapper::_publish(struct imu_sensor_data &data)
 	perf_begin(_accel_sample_perf);
 
 	accel_report accel_report = {};
-	accel_report.timestamp = data.last_read_time_usec;
+	accel_report.timestamp = hrt_absolute_time();
 
 	// TODO: remove these (or get the values)
 	accel_report.x_raw = NAN;
@@ -456,7 +456,7 @@ int DfMpu9250Wrapper::_publish(struct imu_sensor_data &data)
 	perf_begin(_gyro_sample_perf);
 
 	gyro_report gyro_report = {};
-	gyro_report.timestamp = data.last_read_time_usec;
+	gyro_report.timestamp = hrt_absolute_time();
 
 	// TODO: remove these (or get the values)
 	gyro_report.x_raw = NAN;