Configure: use correct variable to infer the .ld file location

We didn't notice the error because it all happened in the top directory.
Now that we use .ld files in subdirectories, the bug became apparent.
Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7347)

Configure

@@ -2079,7 +2079,7 @@ EOF
                 } elsif ($s =~ /\.ld$/) {
                     # We also recognise linker scripts (or corresponding)
                     # We know they are generated files
-                    my $ld = cleanfile($buildd, $s, $blddir);
+                    my $ld = cleanfile($buildd, $_, $blddir);
                     $unified_info{shared_sources}->{$ddest}->{$ld} = 1;
                 } else {
                     die "unrecognised source file type for shared library: $s\n";