Fix for QTMOBILITY-1772 VideoWidget example crash on windows

Fix for QTMOBILITY-1772 VideoWidget example crash on windows

The surface format stride calculation in directshow backend is wrong which results in memory access violation.

Change-Id: I80da5affc9a727513bad9c8d74a9f49d0c1a6c0d
Task-number:QTMOBILITY-1772
Reviewed-by:Michael Goddard
(cherry picked from commit 0b010e781634d3b33750fcead445fc7bd3a6f828)
Reviewed-on: http://codereview.qt.nokia.com/2070
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>