Fix definition of HRESULT in qwindowdefs_win.h.

Task-number: QTBUG-38435
Change-Id: I4a08cd0656fa5d6ecb0b94aa71ca000268835b89
Reviewed-by: Björn Breitmeyer <bjoern.breitmeyer@kdab.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>