[PATCH] zd1211rw: fix potential leak in usb_init

usb_init should call destroy_workqueue when usb_register fails.

Signed-off-by: Maxime Austruy <maxime@tralhalla.org>
Signed-off-by: Ulrich Kunitz <kune@deine-taler.de>
Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>