Fixes the following warnings:
libavdevice/lavfi.c:136:16: warning: assignment discards 'const' qualifier from pointer target type
libavdevice/lavfi.c:137:17: warning: assignment discards 'const' qualifier from pointer target type
{
LavfiContext *lavfi = avctx->priv_data;
AVFilterInOut *input_links = NULL, *output_links = NULL, *inout;
- AVFilter *buffersink, *abuffersink;
+ const AVFilter *buffersink, *abuffersink;
int *pix_fmts = create_all_formats(AV_PIX_FMT_NB);
enum AVMediaType type;
int ret = 0, i, n;