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/ucc_uart.c b/drivers/tty/serial/ucc_uart.c
index f99b0c9..ed047d9 100644
--- a/drivers/tty/serial/ucc_uart.c
+++ b/drivers/tty/serial/ucc_uart.c
@@ -469,7 +469,8 @@
 	int i;
 	unsigned char ch, *cp;
 	struct uart_port *port = &qe_port->port;
-	struct tty_struct *tty = port->state->port.tty;
+	struct tty_port *tport = &port->state->port;
+	struct tty_struct *tty = tport->tty;
 	struct qe_bd *bdp;
 	u16 status;
 	unsigned int flg;
@@ -491,7 +492,7 @@
 		/* If we don't have enough room in RX buffer for the entire BD,
 		 * then we try later, which will be the next RX interrupt.
 		 */
-		if (tty_buffer_request_room(tty, i) < i) {
+		if (tty_buffer_request_room(tport, i) < i) {
 			dev_dbg(port->dev, "ucc-uart: no room in RX buffer\n");
 			return;
 		}