[bfd] Fix data race in bfd_check_format_matches

At the start of bfd_check_format_matches, we have this read of_bfd_section_id:
...
  unsigned int initial_section_id = _bfd_section_id;
...

In order to access the variable, it is required to hold the global BFD lock.

The function already contains code acquiring the lock:
...
  /* Locking is required here in order to manage _bfd_section_id.  */
  if (!bfd_lock ())
    {
      bfd_cache_set_uncloseable (abfd, old_in_format_matches, NULL);
      free (matching_vector);
      return false;
    }
...
so fix this by moving the read after it.

Tested on x86_64-linux.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33826