itg3200: calibrate() doesn't return anything

defect #191

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/itg3200/itg3200.cxx

@@ -81,7 +81,7 @@ Itg3200::~Itg3200()
     mraa_i2c_stop(m_i2c);
 }
 
-mraa_result_t
+void
 Itg3200::calibrate(void)
 {
     int reads = 600;

src/itg3200/itg3200.h

@@ -73,9 +73,8 @@ public:
      * Calibrates the sensor to 0 on all axes. Sensor needs to be resting for accurate calibration.
      * Takes about 3 seconds and is also called by constructor on object creation.
      *
-     * @return 0 for successful calibration
      */
-    mraa_result_t calibrate();
+    void calibrate();
 
     /**
      * Returns the temperature reading from the integrated temperature sensor in Celsius degrees