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>

drivers/tty/pty.c

@@ -123,7 +123,7 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 		c = tty_insert_flip_string(to->port, buf, c);
 		/* And shovel */
 		if (c) {
-			tty_flip_buffer_push(to);
+			tty_flip_buffer_push(to->port);
 			tty_wakeup(tty);
 		}
 	}