USB: FTDI Elan driver: Convert ftdi->u132_lock to mutex

FTDI Elan driver: Convert the semaphore ftdi->u132_lock to the mutex
API

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>