refactor hmc5883: use driver base class

Removes the calibration on startup, as these values were overwritten by
the system calibration values anyway.
So the only difference is that if all calibration scales were equal to 1,
the driver startup would have failed.

boards/airmind/mindpx-v2/init/rc.board_sensors

@@ -6,11 +6,11 @@
 adc start
 
 # External I2C bus
-hmc5883 -C -T -X start
+hmc5883 -T -X start
 qmc5883 -X start
 
 # Internal I2C bus
-hmc5883 -C -T -I -R 12 start
+hmc5883 -T -I -R 12 start
 
 mpu6000 -s -R 8 start
 mpu9250 -s -R 8 start