Fix parameter type

SendMessageTimeout takes a PDWORD_PTR
This fixes compilation on 64 bit.

Change-Id: I5eb1e7fee0c19b48d7f294c1703c104a79ab17ea
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>