ieee802154: rename ieee802154_dev to ieee802154_hw

The identical struct of the wireless stack implementation is named
ieee80211_hw. This is useful to name the variable hw instead of get
confusing with netdev dev variable.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Cc: Alan Ott <alan@signal11.us>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>