Do register the LED mode in onSetup

Without registering it there, the mode will not register, and thus, will not
function either.

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

src/Kaleidoscope/FingerPainter.cpp

@@ -30,6 +30,7 @@ bool FingerPainter::edit_mode_;
 
 EventHandlerResult FingerPainter::onSetup() {
   color_base_ = ::LEDPaletteTheme.reserveThemes(1);
+  ::LEDControl.mode_add(this);
   return EventHandlerResult::OK;
 }