fix a silly typo (1l to myself)

Originally committed as revision 5519 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -653,7 +653,7 @@ for opt do
   case "$opt" in
   --log)
   ;;
-  --log=*) log="${opt#*-}"
+  --log=*) log="${opt#*=}"
   ;;
   --prefix=*) prefix=`echo $opt | cut -d '=' -f 2`; force_prefix=yes
   ;;