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/tty/serial/ifx6x60.c b/drivers/tty/serial/ifx6x60.c
index 4bc6e47..6a6668b 100644
--- a/drivers/tty/serial/ifx6x60.c
+++ b/drivers/tty/serial/ifx6x60.c
@@ -669,12 +669,8 @@
 static void ifx_spi_insert_flip_string(struct ifx_spi_device *ifx_dev,
 				    unsigned char *chars, size_t size)
 {
-	struct tty_struct *tty = tty_port_tty_get(&ifx_dev->tty_port);
-	if (!tty)
-		return;
 	tty_insert_flip_string(&ifx_dev->tty_port, chars, size);
-	tty_flip_buffer_push(tty);
-	tty_kref_put(tty);
+	tty_flip_buffer_push(&ifx_dev->tty_port);
 }
 
 /**