[D3D9] fix for SetFVF memleak [2nd try+patch]

[H. Verbeet]

On 07/10/06, Karsten Elfenbein <kelfe at gmx.de> wrote:
> * don't prevent IUnknown_Release of pDecl in the exit section and fix
> for http://bugs.winehq.org/show_bug.cgi?id=5656
>
As mentioned on IRC, this can't work. Releasing the declaration there
will cause it to be destroyed and break GetVertexDeclaration().
Instead, we should store the declaration we just created and release
it on the next call to either SetVertexDeclaration() or SetFVF(), and
when the device is destroyed.