[Mingw-w64-public] Fix for winreg.h

Hi, I would like to contribute a minor patch to fix RegSetKeyValueW declaration in winreg.h. Please pull the change from https://github.com/janisozaur/mingw-w64 fix-winreg.h I'm not familiar with the process of submitting patches, so please let me know if I need to do something else as well.

[Mingw-w64-public] Fix for winreg.h

Hi, I would like to contribute a minor patch (attached) to fix RegSetKeyValueW declaration in winreg.h. I'm not familiar with the process of submitting patches, so please let me know if I need to do something else as well. Best regards, Michał. -- Michal Janiszewski From 19e04a932735fc9b18e8627b5