serial: timbuart: drop low-latency workaround

The timbuart driver has always carried a workaround for the infamous
low_latency behaviour of tty_flip_buffer_push() which required not
holding the port lock when the low_latency flag was set.

Since commit a9c3f68f3c ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks
around.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210421095509.3024-25-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/timbuart.c

@@ -87,9 +87,7 @@ static void timbuart_rx_chars(struct uart_port *port)
 		tty_insert_flip_char(tport, ch, TTY_NORMAL);
 	}
 
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(tport);
-	spin_lock(&port->lock);
 
 	dev_dbg(port->dev, "%s - total read %d bytes\n",
 		__func__, port->icount.rx);