tty/serial: at91: maxburst was missing for dma transfers

Maxburst was not set when doing the dma slave configuration. This value
is checked by the recently introduced xdmac. It causes an error when
doing the slave configuration and so prevents from using dma.
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: <stable@vger.kernel.org> # 3.12 and later
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -880,6 +880,7 @@ static int atmel_prepare_tx_dma(struct uart_port *port)
 	config.direction = DMA_MEM_TO_DEV;
 	config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
 	config.dst_addr = port->mapbase + ATMEL_US_THR;
+	config.dst_maxburst = 1;
 
 	ret = dmaengine_slave_config(atmel_port->chan_tx,
 				     &config);
@@ -1059,6 +1060,7 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
 	config.direction = DMA_DEV_TO_MEM;
 	config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
 	config.src_addr = port->mapbase + ATMEL_US_RHR;
+	config.src_maxburst = 1;
 
 	ret = dmaengine_slave_config(atmel_port->chan_rx,
 				     &config);