USB: fix locking in idmouse

Pete caused me to lock at buggy drivers in this respect. The idmouse has
a race between open and disconnect. This patch

- solves the open/disconnect race
- switches locking to mutexes

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>