Fix onSetup, to register the LED mode

When using the V1 compatibility layer, in the `onSetup()` method, we need to
call `LEDControl.mode_add()`, otherwise the mode does not register, and will not
function.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/Kaleidoscope/LED-Stalker.h

@@ -40,6 +40,8 @@ class StalkerEffect : public LEDMode {
 
 #if KALEIDOSCOPE_ENABLE_V1_PLUGIN_API
   kaleidoscope::EventHandlerResult onSetup() {
+    ::LEDControl.mode_add(this);
+
     return kaleidoscope::EventHandlerResult::OK;
   }
 #endif