pcmcia: remove pcmcia_add_device_lock

As all cards to pcmcia_device_add() are already locked by skt_mutex, and
the critical sections inside this function are further protected by
ops_mutex, there's no need to keep a third lock around. Therfore, remove
pcmcia_add_device_lock.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>