avdevice/fbdev_dec: use errno instead of ret for av_log

Should fix printing the wrong value
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/fbdev_dec.c

@@ -183,7 +183,7 @@ static int fbdev_read_packet(AVFormatContext *avctx, AVPacket *pkt)
     /* refresh fbdev->varinfo, visible data position may change at each call */
     if (ioctl(fbdev->fd, FBIOGET_VSCREENINFO, &fbdev->varinfo) < 0) {
         av_log(avctx, AV_LOG_WARNING,
-               "Error refreshing variable info: %s\n", av_err2str(ret));
+               "Error refreshing variable info: %s\n", av_err2str(AVERROR(errno)));
     }
 
     pkt->pts = curtime;