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/max3100.c b/drivers/tty/serial/max3100.c
index e238e80..791e1df 100644
--- a/drivers/tty/serial/max3100.c
+++ b/drivers/tty/serial/max3100.c
@@ -311,8 +311,8 @@
 			}
 		}
 
-		if (rxchars > 16 && s->port.state->port.tty != NULL) {
-			tty_flip_buffer_push(s->port.state->port.tty);
+		if (rxchars > 16) {
+			tty_flip_buffer_push(&s->port.state->port);
 			rxchars = 0;
 		}
 		if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
@@ -324,8 +324,8 @@
 		  (!uart_circ_empty(xmit) &&
 		   !uart_tx_stopped(&s->port))));
 
-	if (rxchars > 0 && s->port.state->port.tty != NULL)
-		tty_flip_buffer_push(s->port.state->port.tty);
+	if (rxchars > 0)
+		tty_flip_buffer_push(&s->port.state->port);
 }
 
 static irqreturn_t max3100_irq(int irqno, void *dev_id)