Fix Ext0 motor is not disabled on DaVinci 2.0

Pin is 128 and int8_t see is as -128 and then give the condition to
disable wrong
if(extruder[i].enablePin > -1)
digitalWrite(extruder[i].enablePin,!extruder[i].enableOn);
change type of value to int16_t to avoid 128 and upper pin to be seen as
negative pin

src/ArduinoDUE/Repetier/Extruder.h

@@ -112,7 +112,7 @@ class Extruder   // Size: 12*1 Byte+12*4 Byte+4*2Byte = 68 Byte
     int32_t xOffset;
     int32_t yOffset;
     float stepsPerMM;        ///< Steps per mm.
-    int8_t enablePin;          ///< Pin to enable extruder stepper motor.
+    int16_t enablePin;          ///< Pin to enable extruder stepper motor.
 //  uint8_t directionPin; ///< Pin number to assign the direction.
 //  uint8_t stepPin; ///< Pin number for a step.
     uint8_t enableOn;