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>
diff --git a/drivers/net/irda/irtty-sir.c b/drivers/net/irda/irtty-sir.c
index 6e4d4b6..a412671 100644
--- a/drivers/net/irda/irtty-sir.c
+++ b/drivers/net/irda/irtty-sir.c
@@ -210,7 +210,7 @@
  *    been received, which can now be decapsulated and delivered for
  *    further processing 
  *
- * calling context depends on underlying driver and tty->low_latency!
+ * calling context depends on underlying driver and tty->port->low_latency!
  * for example (low_latency: 1 / 0):
  * serial.c:	uart-interrupt / softint
  * usbserial:	urb-complete-interrupt / softint