staging: kpc2000: remove lock_card/unlock_card functions

We do not need an inline function to "hide" the lock, so just replace
the few calls to these functions with the "real" mutex_lock/unlock()
calls.

Cc: Matt Sickler <Matt.Sickler@daktronics.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>