serial: sh-sci: Don't call sci_dma_rx_push() if no data has arrived

On receive DMA time-out, avoid calling sci_dma_rx_push() if no data was
transferred by the timed out DMA request.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -1467,10 +1467,11 @@ static void work_fn_rx(struct work_struct *work)
 		dev_dbg(port->dev, "Read %u bytes with cookie %d\n", read,
 			s->active_rx);
 
-		count = sci_dma_rx_push(s, s->rx_buf[new], read);
-
-		if (count)
-			tty_flip_buffer_push(&port->state->port);
+		if (read) {
+			count = sci_dma_rx_push(s, s->rx_buf[new], read);
+			if (count)
+				tty_flip_buffer_push(&port->state->port);
+		}
 
 		spin_unlock_irqrestore(&port->lock, flags);