amstream: Constify a variable

[Andrew Talbot]

Changelog:
    amstream: Constify a variable.

diff -urN a/dlls/amstream/mediastream.c b/dlls/amstream/mediastream.c
--- a/dlls/amstream/mediastream.c	2006-10-07 17:37:06.000000000 +0100
+++ b/dlls/amstream/mediastream.c	2007-02-12 17:05:29.000000000 +0000
@@ -42,7 +42,7 @@
     STREAM_TYPE StreamType;
 } IMediaStreamImpl;
 
-static struct IMediaStreamVtbl MediaStream_Vtbl;
+static const struct IMediaStreamVtbl MediaStream_Vtbl;
 
 HRESULT MediaStream_create(IMultiMediaStream* Parent, const MSPID* 
pPurposeId, STREAM_TYPE StreamType, IMediaStream** ppMediaStream)
 {
@@ -166,7 +166,7 @@
     return S_FALSE;
 }
 
-static IMediaStreamVtbl MediaStream_Vtbl =
+static const struct IMediaStreamVtbl MediaStream_Vtbl =
 {
     IMediaStreamImpl_QueryInterface,
     IMediaStreamImpl_AddRef,