[d3d9/tests] Fix size parameter for memcmp (Coccinelle)

[Henri Verbeet]

2010/1/8 Paul Vriens <paul.vriens.wine at gmail.com>:
> -    i = memcmp(decl, vertex_decl, sizeof(vertex_decl));
> +    i = memcmp(decl, vertex_decl, sizeof(*vertex_decl));
I think that should be "num_elements * sizeof(*vertex_decl)" even.