ddraw/tests: Use wine_dbgstr_rect() in the ddraw7 tests.

[Henri Verbeet]

On 8 June 2016 at 23:48, Stefan Dösinger <stefandoesinger at gmail.com> wrote:
>
>> === w864 (32 bit ddraw7) ===
>> ddraw7.c:7911: Test failed: Got unexpected P8 color key blit result.
> Fwiw, this is my recently added test. I'll look at it on the weekend.
>
I was under the impression the original p8_primary_test() failed like
this from time to time as well, although it seems to fail more
reliably now.