USB: use mutex instead of semaphore in the ELAN U132 adapter driver

The ELAN U132 adapter driver uses the semaphore u132_module_lock
as mutex. Use the mutex API instead of the (binary) semaphore.

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