tty: ipwireless: fix error handling

ipwireless_send_packet() can only return 0 on success and -ENOMEM on
error, the caller should check non zero for error condition
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Acked-by: David Sterba <dsterba@suse.com>
Link: https://lore.kernel.org/r/20200821161942.36589-1-ztong0001@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/ipwireless/network.c

@@ -117,7 +117,7 @@ static int ipwireless_ppp_start_xmit(struct ppp_channel *ppp_channel,
 					       skb->len,
 					       notify_packet_sent,
 					       network);
-			if (ret == -1) {
+			if (ret < 0) {
 				skb_pull(skb, 2);
 				return 0;
 			}
@@ -134,7 +134,7 @@ static int ipwireless_ppp_start_xmit(struct ppp_channel *ppp_channel,
 					       notify_packet_sent,
 					       network);
 			kfree(buf);
-			if (ret == -1)
+			if (ret < 0)
 				return 0;
 		}
 		kfree_skb(skb);

drivers/tty/ipwireless/tty.c

@@ -218,7 +218,7 @@ static int ipw_write(struct tty_struct *linux_tty,
 	ret = ipwireless_send_packet(tty->hardware, IPW_CHANNEL_RAS,
 			       buf, count,
 			       ipw_write_packet_sent_callback, tty);
-	if (ret == -1) {
+	if (ret < 0) {
 		mutex_unlock(&tty->ipw_tty_mutex);
 		return 0;
 	}