radv/video: Fix msg header total size

It needs to include also codec msg size.

Cc: mesa-stable
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34449>

src/amd/vulkan/radv_video.c

@@ -2040,6 +2040,8 @@ rvcn_dec_message_decode(struct radv_cmd_buffer *cmd_buffer, struct radv_video_se
       unreachable("unknown operation");
    }
 
+   header->total_size += index_codec->size;
+
    if (dpb_update_required)
       assert(frame_info->pSetupReferenceSlot != NULL);