net: ieee802154: fix a potential NULL pointer dereference

In case alloc_ordered_workqueue fails, the fix releases
sources and returns -ENOMEM to avoid NULL pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>