TTY: switch tty_buffer_request_room to tty_port

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty pointer in
many call sites. Only tty_port will be needed and hence no more
tty_port_tty_get calls in those paths.

Here we start with tty_buffer_request_room.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/mpsc.c b/drivers/tty/serial/mpsc.c
index 6a9c660..5036686 100644
--- a/drivers/tty/serial/mpsc.c
+++ b/drivers/tty/serial/mpsc.c
@@ -937,7 +937,8 @@
 static int mpsc_rx_intr(struct mpsc_port_info *pi)
 {
 	struct mpsc_rx_desc *rxre;
-	struct tty_struct *tty = pi->port.state->port.tty;
+	struct tty_port *port = &pi->port.state->port;
+	struct tty_struct *tty = port->tty;
 	u32	cmdstat, bytes_in, i;
 	int	rc = 0;
 	u8	*bp;
@@ -968,8 +969,7 @@
 		}
 #endif
 		/* Following use of tty struct directly is deprecated */
-		if (unlikely(tty_buffer_request_room(tty, bytes_in)
-					< bytes_in)) {
+		if (tty_buffer_request_room(port, bytes_in) < bytes_in) {
 			if (tty->low_latency)
 				tty_flip_buffer_push(tty);
 			/*