mpeg4vdpau: Fix priv data size.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/mpeg4videodec.c

@@ -2795,7 +2795,7 @@ AVCodec ff_mpeg4_vdpau_decoder = {
     .long_name      = NULL_IF_CONFIG_SMALL("MPEG-4 part 2 (VDPAU)"),
     .type           = AVMEDIA_TYPE_VIDEO,
     .id             = AV_CODEC_ID_MPEG4,
-    .priv_data_size = sizeof(MpegEncContext),
+    .priv_data_size = sizeof(Mpeg4DecContext),
     .init           = decode_init,
     .close          = ff_h263_decode_end,
     .decode         = ff_h263_decode_frame,