cngenc: Remove dead store

ff_lpc_calc_ref_coeffs returns the order it is given and cannot return
in error.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavcodec/cngenc.c

@@ -91,7 +91,7 @@ static int cng_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
     } else {
         qdbov = 127;
     }
-    ret = ff_lpc_calc_ref_coefs(&p->lpc, p->samples32, p->order, p->ref_coef);
+    ff_lpc_calc_ref_coefs(&p->lpc, p->samples32, p->order, p->ref_coef);
     avpkt->data[0] = qdbov;
     for (i = 0; i < p->order; i++)
         avpkt->data[1 + i] = p->ref_coef[i] * 127 + 127;