checksrc.pl: add quotes to var

lib/checksrc.pl

@@ -79,7 +79,7 @@ if(!$file) {
 }
 
 do {
-    if($wlist !~ / $file /) {
+    if("$wlist" !~ / $file /) {
         my $fullname = $file;
         $fullname = "$dir/$file" if ($fullname !~ '^\.?\.?/');
         scanfile($fullname);