staging/lustre/lov: Remove unused lov_lsm_decref()

Also lov_lsm_addref is only used in the file it is defined,
so make it static

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