staging/lustre/ldlm: Remove ldlm_namespace_inactive_list()

Since there are no server namespaces, just replace it with
ldlm_cli_inactive_namespace_list pointer.
Also make ldlm_cli_inactive_namespace_list static as it's only
used in ldlm_resource.c

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>