Class was destroyed before starting the unregistering driver chain.
Disconnecting a device from roccat chardev in this process then
raised a NULL pointer dereference.
Fixed this by destroying class after unregistering driver.
Signed-off-by: Stefan Achatz <erazor_de@users.sourceforge.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>