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/ehv_bytechan.c b/drivers/tty/ehv_bytechan.c
index c117d77..af97e39 100644
--- a/drivers/tty/ehv_bytechan.c
+++ b/drivers/tty/ehv_bytechan.c
@@ -386,7 +386,7 @@
 	 * read from the byte channel will be accepted by the TTY layer.
 	 */
 	ev_byte_channel_poll(bc->handle, &rx_count, &tx_count);
-	count = tty_buffer_request_room(ttys, rx_count);
+	count = tty_buffer_request_room(&bc->port, rx_count);
 
 	/* 'count' is the maximum amount of data the TTY layer can accept at
 	 * this time.  However, during testing, I was never able to get 'count'