dwrite: Fix transform matrix usage for pixel snapping

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=15314

Your paranoid android.


=== wvistau64 (64 bit layout) ===
layout.c:3395: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859

=== w2008s64 (64 bit layout) ===
layout.c:3395: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859
layout.c:3408: Test failed: 27: got 12.001999, expected 12.002001, baseline 12.005859