mac802154: rename hw subif_data variable to local

This patch renames the hw attribute in struct ieee802154_sub_if_data to
local. This avoid confusing with the struct ieee802154_hw hw; inside of
local struct.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>