benchmark.pl: replace use of Perl <> with <<>>.

I've only just found out that it has the effect of treating the argv
words not as plain filenames, but as arguments to Perl default 'open',
i.e. if they end in | then the text before that is treated as a
command. That's not what was intended!

benchmark.pl

@@ -9,7 +9,7 @@ my @presets = ();
 my %presets = ();
 my $maxval = 0;
 
-while (<>) {
+while (<<>>) {
     chomp;
     if (/^(.*)(#.*): ([\d\.]+)$/) {
         push @presets, $1 unless defined $presets{$1};