TTY: switch tty_flip_buffer_push

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

Now, the one where most of tty_port_tty_get gets removed:
tty_flip_buffer_push.

IOW we also closed all the races in drivers not using tty_port_tty_get
at all yet.

Also we move tty_flip_buffer_push declaration from include/linux/tty.h
to include/linux/tty_flip.h to all others while we are changing it
anyway.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/serial/quatech2.c b/drivers/usb/serial/quatech2.c
index 5dccc4f..6850745 100644
--- a/drivers/usb/serial/quatech2.c
+++ b/drivers/usb/serial/quatech2.c
@@ -609,7 +609,6 @@
 	struct qt2_serial_private *serial_priv;
 	struct usb_serial_port *port;
 	struct qt2_port_private *port_priv;
-	struct tty_struct *tty;
 	bool escapeflag;
 	unsigned char *ch;
 	int i;
@@ -620,15 +619,11 @@
 		return;
 
 	ch = urb->transfer_buffer;
-	tty = NULL;
 	serial = urb->context;
 	serial_priv = usb_get_serial_data(serial);
 	port = serial->port[serial_priv->current_port];
 	port_priv = usb_get_serial_port_data(port);
 
-	if (port_priv->is_open)
-		tty = tty_port_tty_get(&port->port);
-
 	for (i = 0; i < urb->actual_length; i++) {
 		ch = (unsigned char *)urb->transfer_buffer + i;
 		if ((i <= (len - 3)) &&
@@ -666,10 +661,7 @@
 						 __func__);
 					break;
 				}
-				if (tty) {
-					tty_flip_buffer_push(tty);
-					tty_kref_put(tty);
-				}
+				tty_flip_buffer_push(&port->port);
 
 				newport = *(ch + 3);
 
@@ -683,10 +675,6 @@
 				serial_priv->current_port = newport;
 				port = serial->port[serial_priv->current_port];
 				port_priv = usb_get_serial_port_data(port);
-				if (port_priv->is_open)
-					tty = tty_port_tty_get(&port->port);
-				else
-					tty = NULL;
 				i += 3;
 				escapeflag = true;
 				break;
@@ -716,10 +704,7 @@
 		tty_insert_flip_string(&port->port, ch, 1);
 	}
 
-	if (tty) {
-		tty_flip_buffer_push(tty);
-		tty_kref_put(tty);
-	}
+	tty_flip_buffer_push(&port->port);
 }
 
 static void qt2_write_bulk_callback(struct urb *urb)