If you want to test more than one time at a time, then you need to store more than one line in memory. The two most straightforward approaches here would be to cache the previous line:

my $last = '';
while (my $line = <$fh>) {
    if (    $last =~ m/USB\d*::0x[0-9a-fA-F::]+0x[0-9a-fA-F]+::[0-9a-f
+A-F]+INSTR$/ 
        and $line =~ m/USB\d*::0x[0-9a-fA-F::]+0x[0-9a-fA-F]+::[0-9a-f
+A-F]+INSTR$/) 
    {
        print "$last$line";
    }
    $last = $line;
}
[download]

or slurp the whole file and then grab the chunk you are interested in:

my $content = do{local $/;<$fh>};
while ($content =~ /((?:USB\d*::0x[0-9a-fA-F::]+0x[0-9a-fA-F]+::[0-9a-
+fA-F]+INSTR\n){2})/g) {
    print $1;
}
[download]

I should mention that your posted regex is inconsistent with what I'm presuming your text looks like, so you should post your input file, wrapped in code tags so whitespace doesn't get mangled. You should also be aware that \s*(.+?)\s* will require at least 1 non-newline character in the text joining your two lines, since without the s modifer, . won't match a newline.