avcodec/pcm-dvdenc: don't allow the user to set frame_size

This is for an upcoming change where the field will become user settable.
Unless a proper check for frame_size is introduced, it's better to just not
allow arbitrary values to be used.

Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/pcm-dvdenc.c

@@ -106,8 +106,7 @@ static av_cold int pcm_dvd_encode_init(AVCodecContext *avctx)
     s->header[1] = (quant << 6) | (freq << 4) | (avctx->ch_layout.nb_channels - 1);
     s->header[2] = 0x80;
 
-    if (!avctx->frame_size)
-        avctx->frame_size = frame_size;
+    avctx->frame_size = frame_size;
 
     return 0;
 }