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/apbuart.c b/drivers/tty/serial/apbuart.c
index 59ae2b5..6331464 100644
--- a/drivers/tty/serial/apbuart.c
+++ b/drivers/tty/serial/apbuart.c
@@ -78,7 +78,6 @@
 
 static void apbuart_rx_chars(struct uart_port *port)
 {
-	struct tty_struct *tty = port->state->port.tty;
 	unsigned int status, ch, rsr, flag;
 	unsigned int max_chars = port->fifosize;
 
@@ -126,7 +125,7 @@
 		status = UART_GET_STATUS(port);
 	}
 
-	tty_flip_buffer_push(tty);
+	tty_flip_buffer_push(&port->state->port);
 }
 
 static void apbuart_tx_chars(struct uart_port *port)