at86rf230: remove unnecessary assign

The attribute extra_tx_headroom should already be zero.
Signed-off-by: NAlexander Aring <alex.aring@gmail.com>
Reviewed-by: NStefan Schmidt <s.schmidt@samsung.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/at86rf230.c

@@ -1431,7 +1431,6 @@ at86rf230_detect_device(struct at86rf230_local *lp)
 		return -EINVAL;
 	}
 
-	lp->hw->extra_tx_headroom = 0;
 	lp->hw->flags = IEEE802154_HW_TX_OMIT_CKSUM | IEEE802154_HW_AACK |
 			IEEE802154_HW_TXPOWER | IEEE802154_HW_ARET |
 			IEEE802154_HW_AFILT | IEEE802154_HW_PROMISCUOUS;