[nostalgia/core] Add Context buttonDown function

src/nostalgia/core/gba/core.cpp

@@ -55,7 +55,7 @@ uint64_t ticksMs(Context*) noexcept {
 	return g_timerMs;
 }
 
-bool buttonDown(Key k) noexcept {
+bool buttonDown(Context*, Key k) noexcept {
 	return !(REG_GAMEPAD & k);
 }