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/tty/serial/mrst_max3110.c b/drivers/tty/serial/mrst_max3110.c
index 3b8df7b..4632db7 100644
--- a/drivers/tty/serial/mrst_max3110.c
+++ b/drivers/tty/serial/mrst_max3110.c
@@ -495,7 +495,7 @@
 			| WC_BAUD_DR2;
 
 	/* as we use thread to handle tx/rx, need set low latency */
-	port->state->port.tty->low_latency = 1;
+	port->state->port.low_latency = 1;
 
 	if (max->irq) {
 		max->read_thread = NULL;