ieee802154: fix one possible memleak in adf7242_probe

When probe fail, we should destroy the workqueue.

Fixes: 2795e8c2 ("net: ieee802154: fix a potential NULL pointer dereference")
Signed-off-by: Liu Jian <liujian56@huawei.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Link: https://lore.kernel.org/r/20200717090121.2143-1-liujian56@huawei.com


Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>