Fix compile warning on Windows

Reviewed-by: Prasanth Ullattil
(cherry picked from commit 800ad68e4f000e65b0a83ef1da2a29d595964156)

src/corelib/io/qfilesystemengine_win.cpp

@@ -583,6 +583,7 @@ QString QFileSystemEngine::owner(const QFileSystemEntry &entry, QAbstractFileEng
         }
     }
 #else
+    Q_UNUSED(entry);
     Q_UNUSED(own);
 #endif
     return name;