driver/mcu/ATmega32U4: Fix the class declaration for virtual builds

Due to the introduction of MCU properties recently, we need to declare the class
for virtual builds, and can't get away with simply typedefing it to Base.

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

src/kaleidoscope/driver/mcu/ATmega32U4.h

@@ -64,7 +64,8 @@ class ATmega32U4 : public kaleidoscope::driver::mcu::Base {
   void setup() {}
 };
 #else
-typedef Base ATmega32U4;
+template <typename _Props>
+class ATmega32U4 : public kaleidoscope::driver::mcu::Base<_Props> {};
 #endif // ifndef KALEIDOSCOPE_VIRTUAL_BUILD
 
 }