ieee802154: fix error return code in ieee802154_add_iface()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: be51da0f

 ("ieee802154: Stop using NLA_PUT*().")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20210508062517.2574-1-thunder.leizhen@huawei.com


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