serial_core: Fix conditional start_tx on ring buffer not empty

If the serial_core ring buffer empties just as the tty layer receives an XOFF, then start_tx will never be called when the tty layer receives an XON as the serial_core ring buffer is empty. This will possibly leave a few bytes trapped in the fifo for drivers that disable the transmitter when flow controlled.

---
 drivers/tty/serial/serial_core.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index ece2049..b3e5907 100644
@@ -89,8 +89,7 @@ static void __uart_start(struct tty_struct *tty)
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port = state->uart_port;
 
-	if (!uart_circ_empty(&state->xmit) && state->xmit.buf &&
-	    !tty->stopped && !tty->hw_stopped)
+	if (!tty->stopped && !tty->hw_stopped)
 		port->ops->start_tx(port);
 }
 

1.7.10.4