libmp3lame: Fix assignments in if()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libmp3lame.c

@@ -237,7 +237,7 @@ static int mp3lame_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
 
     /* add current frame to the queue */
     if (frame) {
-        if ((ret = ff_af_queue_add(&s->afq, frame) < 0))
+        if ((ret = ff_af_queue_add(&s->afq, frame)) < 0)
             return ret;
     }