csr1212_keep_keyval(kv) in nodemgr_process_root_directory was
unbalanced if ne->vendor_name_kv already exists.  This happens for
example if eth1394 or raw1394 modify the local config ROM and it is
parsed again.

As a bonus, the attempt to add the vendor_name_kv sysfs attribute
when it already exists is now fixed for good.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>