[clang-tidy] use override instead of virtual

Found with modernize-use-override

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/filter/plugins/NormalizeFilterPlugin.cxx

@@ -38,7 +38,7 @@ public:
 		:Filter(audio_format), compressor(Compressor_new(0)) {
 	}
 
-	~NormalizeFilter() {
+	~NormalizeFilter() override {
 		Compressor_delete(compressor);
 	}
 

src/filter/plugins/NullFilterPlugin.cxx

@@ -32,7 +32,7 @@
 
 class PreparedNullFilter final : public PreparedFilter {
 public:
-	virtual std::unique_ptr<Filter> Open(AudioFormat &af) override {
+	std::unique_ptr<Filter> Open(AudioFormat &af) override {
 		return std::make_unique<NullFilter>(af);
 	}
 };