[sim] SimDataValue: Fix cancellation

The uid was getting incremented by 1 during registration but not decremented
by 1 during cancellation, so cancellation didn't work correctly.

As the underlying registration ensures a non-zero result, don't increment
the result.

hal/src/main/native/include/hal/simulation/SimDataValue.h

@@ -53,7 +53,7 @@ class SimDataValueBase : protected SimCallbackRegistryBase {
       lock.unlock();
       callback(name, param, &value);
     }
-    return newUid + 1;
+    return newUid;
   }
 
   void DoSet(T value, const char* name) {