Return defaultValue from defaultEmit()

`value` was never passed and would be undefined.

Fixes #7016

Author: samme

src/gameobjects/particles/EmitterOp.js

@@ -599,15 +599,11 @@ var EmitterOp = new Class({
      * @method Phaser.GameObjects.Particles.EmitterOp#defaultEmit
      * @since 3.0.0
      *
-     * @param {Phaser.GameObjects.Particles.Particle} particle - The particle.
-     * @param {string} key - The name of the property.
-     * @param {number} [value] - The current value of the property.
-     *
      * @return {number} The new value of the property.
      */
-    defaultEmit: function (particle, key, value)
+    defaultEmit: function ()
     {
-        return value;
+        return this.defaultValue;
     },
 
     /**