Get rid of semaphore abuse by converting device_driver->unload_sem
semaphore to device_driver->unloaded completion.

This should get rid of any confusion as well as save a few bytes in the
process.
Signed-off-by: Mike Waychison <michael.waychison@sun.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>