p910nd: Fix the lock directory use

The original code uses a subdir inside of /var/lock which is hard for
us to manage as it may be running in tmpfs; we did change it for avoid
the subdir so it just works.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>