fix warning on MSVC
fix warning on MSVC

 'function' : different 'const' qualifiers

Change-Id: I855e94e8734a7e9a6156c771a7bad41b19a450d7

webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp