file_sys/nsp: Make SetTicketKeys actually do something

Previously, the method wasn't modifying any class state and therefore not having any effects when called.
Since this has been the case for a very long time now, I'm not sure if we couldn't just remove this method altogether.

src/core/file_sys/submission_package.h

@@ -59,6 +59,7 @@ public:
     VirtualDir GetParentDirectory() const override;
 
 private:
+    void SetTicketKeys(const std::vector<VirtualFile>& files);
     void InitializeExeFSAndRomFS(const std::vector<VirtualFile>& files);
     void ReadNCAs(const std::vector<VirtualFile>& files);