regtests: use bitrate syntax understood by both tools

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

tests/lavf-regression.sh

@@ -53,7 +53,7 @@ fi
 
 if [ -n "$do_rm" ] ; then
 file=${outfile}lavf.rm
-do_avconv $file $DEC_OPTS -f image2 -vcodec pgmyuv -i $raw_src $DEC_OPTS -ar 44100 -f s16le -i $pcm_src $ENC_OPTS -t 1 -qscale 10 -acodec ac3_fixed -b:a 64k
+do_avconv $file $DEC_OPTS -f image2 -vcodec pgmyuv -i $raw_src $DEC_OPTS -ar 44100 -f s16le -i $pcm_src $ENC_OPTS -t 1 -qscale 10 -acodec ac3_fixed -ab 64k
 # broken
 #do_avconv_crc $file -i $target_path/$file
 fi