atmel_serial: fix flow control bug

Fix the following problem, related to hardware flow control (CTS/RTS):
Transmitting while CTS line is asserted in DMA mode, due to not checking
for tx-stopped condition.

We found these problems while testing the UARTs with hardware
flow-control.
Signed-off-by: NHaavard Skinnemoen <haavard.skinnemoen@atmel.com>
Cc: "Andrew Victor" <avictor.za@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/serial/atmel_serial.c

@@ -579,7 +579,7 @@ static void atmel_tx_dma(struct uart_port *port)
 	/* disable PDC transmit */
 	UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
 
-	if (!uart_circ_empty(xmit)) {
+	if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
 		dma_sync_single_for_device(port->dev,
 					   pdc->dma_addr,
 					   pdc->dma_size,