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/s390/char/sclp_vt220.c b/drivers/s390/char/sclp_vt220.c
index 0eca99b..6c92f62 100644
--- a/drivers/s390/char/sclp_vt220.c
+++ b/drivers/s390/char/sclp_vt220.c
@@ -461,14 +461,9 @@
 static void
 sclp_vt220_receiver_fn(struct evbuf_header *evbuf)
 {
-	struct tty_struct *tty = tty_port_tty_get(&sclp_vt220_port);
 	char *buffer;
 	unsigned int count;
 
-	/* Ignore input if device is not open */
-	if (tty == NULL)
-		return;
-
 	buffer = (char *) ((addr_t) evbuf + sizeof(struct evbuf_header));
 	count = evbuf->length - sizeof(struct evbuf_header);
 
@@ -481,10 +476,9 @@
 		buffer++;
 		count--;
 		tty_insert_flip_string(&sclp_vt220_port, buffer, count);
-		tty_flip_buffer_push(tty);
+		tty_flip_buffer_push(&sclp_vt220_port);
 		break;
 	}
-	tty_kref_put(tty);
 }
 
 /*