This matches the declaration with official documentation and fixes
the following two compiler errors in apitrace project.

d3d9trace.cpp:28469:59: error: invalid conversion from 'const DXVA2_ConfigPictureDecode*' to 'DXVA2_ConfigPictureDecode*' [-fpermissive]
d3d9trace.cpp:28194:65: error: invalid conversion from 'void*' to 'IUnknown*' [-fpermissive]
Signed-off-by: Biswapriyo Nath <nathbappai@gmail.com>