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/sierra.c b/drivers/usb/serial/sierra.c
index 64e53fd..70aee8d 100644
--- a/drivers/usb/serial/sierra.c
+++ b/drivers/usb/serial/sierra.c
@@ -569,7 +569,6 @@
 	int err;
 	int endpoint;
 	struct usb_serial_port *port;
-	struct tty_struct *tty;
 	unsigned char *data = urb->transfer_buffer;
 	int status = urb->status;
 
@@ -581,16 +580,12 @@
 			" endpoint %02x\n", __func__, status, endpoint);
 	} else {
 		if (urb->actual_length) {
-			tty = tty_port_tty_get(&port->port);
-			if (tty) {
-				tty_insert_flip_string(&port->port, data,
-					urb->actual_length);
-				tty_flip_buffer_push(tty);
+			tty_insert_flip_string(&port->port, data,
+				urb->actual_length);
+			tty_flip_buffer_push(&port->port);
 
-				tty_kref_put(tty);
-				usb_serial_debug_data(&port->dev, __func__,
-						      urb->actual_length, data);
-			}
+			usb_serial_debug_data(&port->dev, __func__,
+					      urb->actual_length, data);
 		} else {
 			dev_dbg(&port->dev, "%s: empty read urb"
 				" received\n", __func__);