tsl2561: change getLux calls to return an int

To follow with our simple API requirements, change the return value of getLux()
call to an int. This lets SWIG do a better job with generating an API

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/tsl2561/tsl2561.h

@@ -128,11 +128,9 @@ class TSL2561{
        /**
         * Get calculated lux reading from TSL2561
         *
-        * @param lux - place holder to receive calculated lux value from TSL2561
-        *
-        * Return mraa_result_t
+        * @return the calculated lux value from the sensor
         */
-        mraa_result_t getLux(int &lux);
+        int getLux();
 
     private:
        /**