ac3: fix memleak in fixed-point encoder

caused by typo in mdct_end

libavcodec/ac3enc_fixed.c

@@ -36,7 +36,7 @@
  */
 static av_cold void mdct_end(AC3MDCTContext *mdct)
 {
-    ff_fft_end(&mdct->fft);
+    ff_mdct_end(&mdct->fft);
 }