simplify spi_sync() calling convention

@@ -539,10 +539,7 @@ static void spi_complete(void *arg)
  * Also, the caller is guaranteeing that the memory associated with the
  * message will not be freed before this call returns.
  *
- * The return value is a negative error code if the message could not be
- * submitted, else zero.  When the value is zero, then message->status is
- * also defined;  it's the completion code for the transfer, either zero
- * or a negative error code from the controller driver.
+ * It returns zero on success, else a negative error code.
  */
 int spi_sync(struct spi_device *spi, struct spi_message *message)
 {

@@ -552,8 +549,10 @@ int spi_sync(struct spi_device *spi, str
 	message->complete = spi_complete;
 	message->context = &done;
 	status = spi_async(spi, message);
-	if (status == 0)
+	if (status == 0) {
 		wait_for_completion(&done);
+		status = message->status;
+	}
 	message->context = NULL;
 	return status;
 }

@@ -626,10 +625,8 @@ int spi_write_then_read(struct spi_devic
 
 	/* do the i/o */
 	status = spi_sync(spi, &message);
-	if (status == 0) {
+	if (status == 0)
 		memcpy(rxbuf, x[1].rx_buf, n_rx);
-		status = message.status;
-	}
 
 	if (x[0].tx_buf == buf)
 		up(&lock);