avutil/tx: remove deadcode of the control flow

Fix CID: 1497864
The control flow should return ENOSYS if nb_cd_matches is 0 at before
and the ret equal AVERROR(ENOMEM) or goto end label, so remove the last
control flow if (ret >= 0) before end label.

Signed-off-by: Steven Liu <liuqi05@kuaishou.com>

libavutil/tx.c

@@ -601,9 +601,6 @@ av_cold int ff_tx_init_subtx(AVTXContext *s, enum AVTXType type,
 
     av_free(sub);
 
-    if (ret >= 0)
-        ret = AVERROR(ENOSYS);
-
 end:
     av_free(cd_matches);
     return ret;