TTY: switch tty_buffer_request_room to tty_port

Now, we start converting tty buffer functions to actually use
tty_port. This will allow us to get rid of the need of tty pointer in
many call sites. Only tty_port will be needed and hence no more
tty_port_tty_get calls in those paths.

Here we start with tty_buffer_request_room.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/ioc4_serial.c b/drivers/tty/serial/ioc4_serial.c
index c4e30b8..710ce87 100644
--- a/drivers/tty/serial/ioc4_serial.c
+++ b/drivers/tty/serial/ioc4_serial.c
@@ -2356,7 +2356,7 @@
 	spin_lock_irqsave(&the_port->lock, pflags);
 	tty = state->port.tty;
 
-	request_count = tty_buffer_request_room(tty, IOC4_MAX_CHARS);
+	request_count = tty_buffer_request_room(&state->port, IOC4_MAX_CHARS);
 
 	if (request_count > 0) {
 		icount = &the_port->icount;