Convert a semaphore into a completion in device.c.

Cc: David Teigland <teigland@redhat.com>
Cc: Andrew Morton <akpm@osdl.org>
Signed-off-by: NPatrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>