can: isotp: isotp_sendmsg(): fix return error fix on TX path

With commit d674a8f123b4 ("can: isotp: isotp_sendmsg(): fix return error on FC timeout on TX path") the missing correct return value in the case of a protocol error was introduced.

But the way the error value has been read and sent to the user space does not follow the common scheme to clear the error after reading which is provided by the sock_error() function. This leads to an error report at the following write() attempt although everything should be working.

---
 net/can/isotp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index 84f9aba02901..ca9d728d6d72 100644
@@ -1110,12 +1110,13 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 		/* wait for complete transmission of current pdu */
 		err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
 		if (err)
 			goto err_event_drop;
 
-		if (sk->sk_err)
-			return -sk->sk_err;
+		err = sock_error(sk);
+		if (err)
+			return err;
 	}
 
 	return size;
 
 err_event_drop:

2.30.2