serial: atmel: don't enable IRQs prematurely

The atmel_complete_tx_dma() function disables IRQs at the start
of the function by calling spin_lock_irqsave(&port->lock, flags);
There is no need to disable them a second time using the
spin_lock_irq() function and, in fact, doing so is a bug because
it will enable IRQs prematurely when we call spin_unlock_irq().

Just use spin_lock/unlock() instead without disabling or enabling
IRQs.

Fixes: 08f738b ("serial: at91: add tx dma support")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Acked-by: Richard Genoud <richard.genoud@gmail.com>
Link: https://lore.kernel.org/r/cb7c39a9-c004-4673-92e1-be4e34b85368@moroto.mountain
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dan Carpenter

drivers/tty/serial/atmel_serial.c

@@ -868,11 +868,11 @@ static void atmel_complete_tx_dma(void *arg)
 		dmaengine_terminate_all(chan);
 	uart_xmit_advance(port, atmel_port->tx_len);
 
-	spin_lock_irq(&atmel_port->lock_tx);
+	spin_lock(&atmel_port->lock_tx);
 	async_tx_ack(atmel_port->desc_tx);
 	atmel_port->cookie_tx = -EINVAL;
 	atmel_port->desc_tx = NULL;
-	spin_unlock_irq(&atmel_port->lock_tx);
+	spin_unlock(&atmel_port->lock_tx);
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(port);