linux-wandboard

nl802154: fix Oops in ieee802154_nl_get_dev

ieee802154_nl_get_dev() lacks check for the existance of the device
that was returned by dev_get_XXX, thus resulting in Oops for non-existing
devices. Fix it.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>