greybus: es2: fix arpc return value

ARPC should return 0 on success, but instead was returning the number of
jiffies left until the timeout.

This caused cport_reset() to report an error and an incorrect error
message to be printed when disabling a connection.
Reported-by: NAlex Elder <elder@linaro.org>
Signed-off-by: NJohan Hovold <johan@hovoldconsulting.com>
Tested-by: NAlex Elder <elder@linaro.org>
Signed-off-by: NAlex Elder <elder@linaro.org>

drivers/staging/greybus/es2.c

@@ -1204,6 +1204,8 @@ static int arpc_sync(struct es2_ap_dev *es2, u8 type, void *payload,
 	*result = rpc->resp->result;
 	if (*result)
 		retval = -EREMOTEIO;
+	else
+		retval = 0;
 
 out_arpc_del:
 	spin_lock_irqsave(&es2->arpc_lock, flags);