HMC5883: Silence chatty boot

src/drivers/hmc5883/hmc5883.cpp

@@ -1281,8 +1281,12 @@ int HMC5883::check_calibration()
 	bool scale_valid  = (check_scale() == OK);
 
 	if (_calibrated != (offset_valid && scale_valid)) {
-		warnx("mag cal status changed %s%s", (scale_valid) ? "" : "scale invalid ",
-		      (offset_valid) ? "" : "offset invalid");
+		// too verbose for normal operation
+		if (!offset_valid || !scale_valid) {
+			warnx("mag cal status changed %s%s", (scale_valid) ? "" : "scale invalid ",
+			      (offset_valid) ? "" : "offset invalid");
+		}
+
 		_calibrated = (offset_valid && scale_valid);
 	}