TTY: move low_latency to tty_port

One point is to have less places where we actually need tty pointer.
The other is that low_latency is bound to buffer processing and
buffers are now in tty_port. So it makes sense to move low_latency to
tty_port too.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/ia64/hp/sim/simserial.c

@@ -436,7 +436,7 @@ static int rs_open(struct tty_struct *tty, struct file * filp)
 	struct tty_port *port = &info->port;
 
 	tty->driver_data = info;
-	tty->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
+	port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
 
 	/*
 	 * figure out which console to use (should be one already)