rasterizer_cache: Add missing virtual destructor to RasterizerCacheObject

Ensures that destruction will always do the right thing in any context.

src/video_core/rasterizer_cache.cpp

@@ -0,0 +1,7 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "video_core/rasterizer_cache.h"
+
+RasterizerCacheObject::~RasterizerCacheObject() = default;