ieee802154: cc2520: add rc code in cc2520_tx()

The rc code is 0 at the error path "status & CC2520_STATUS_TX_UNDERFLOW".
Assign rc code with '-EINVAL' at this error path to fix it.
Signed-off-by: Li Qiong <liqiong@nfschina.com>
Link: https://lore.kernel.org/r/20220829071259.18330-1-liqiong@nfschina.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

drivers/net/ieee802154/cc2520.c

@@ -504,6 +504,7 @@ cc2520_tx(struct ieee802154_hw *hw, struct sk_buff *skb)
 		goto err_tx;
 
 	if (status & CC2520_STATUS_TX_UNDERFLOW) {
+		rc = -EINVAL;
 		dev_err(&priv->spi->dev, "cc2520 tx underflow exception\n");
 		goto err_tx;
 	}