stepmotor: various functions should return a value

defects 386, 387

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

src/stepmotor/stepmotor.cxx

 mraa_result_t
 StepMotor::stepForward (int ticks) {
     dirForward ();
-    move (ticks);
+    return move (ticks);
 }
 
 mraa_result_t
 StepMotor::stepBackwards (int ticks) {
     dirBackwards ();
-    move (ticks);
+    return move (ticks);
 }
 
 mraa_result_t