tipc: add missing dev_put() on error in tipc_enable_l2_media

when tipc_own_id failed to obtain node identity,dev_put should
be call before return -EINVAL.

Fixes: 682cd3cf ("tipc: confgiure and apply UDP bearer MTU on running links")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>