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/synclink_gt.c b/drivers/tty/synclink_gt.c
index 9a0358a..fced6ac 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -1854,7 +1854,6 @@
  */
 static void rx_async(struct slgt_info *info)
 {
- 	struct tty_struct *tty = info->port.tty;
  	struct mgsl_icount *icount = &info->icount;
 	unsigned int start, end;
 	unsigned char *p;
@@ -1915,8 +1914,8 @@
 			break;
 	}
 
-	if (tty && chars)
-		tty_flip_buffer_push(tty);
+	if (chars)
+		tty_flip_buffer_push(&info->port);
 }
 
 /*