ca8210: Fix unsigned mac_len comparison with zero in ca8210_skb_tx()

mac_len is of type unsigned, which can never be less than zero.

	mac_len = ieee802154_hdr_peek_addrs(skb, &header);
	if (mac_len < 0)
		return mac_len;

Change this to type int as ieee802154_hdr_peek_addrs() can return negative
integers, this is found by static analysis with smatch.

Fixes: 6c99377 ("ca8210: fix mac_len negative array access")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230306191824.4115839-1-harshit.m.mogalapalli@oracle.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

drivers/net/ieee802154/ca8210.c

@@ -1902,10 +1902,9 @@ static int ca8210_skb_tx(
 	struct ca8210_priv  *priv
 )
 {
-	int status;
 	struct ieee802154_hdr header = { };
 	struct secspec secspec;
-	unsigned int mac_len;
+	int mac_len, status;
 
 	dev_dbg(&priv->spi->dev, "%s called\n", __func__);