TTY: convert more flipping functions

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.

Now 4 string flipping ones are on turn:
* tty_insert_flip_string_flags
* tty_insert_flip_string_fixed_flag
* tty_prepare_flip_string
* tty_prepare_flip_string_flags

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/pl2303.c

@@ -812,7 +812,7 @@ static void pl2303_process_read_urb(struct urb *urb)
 			if (!usb_serial_handle_sysrq_char(port, data[i]))
 				tty_insert_flip_char(tty, data[i], tty_flag);
 	} else {
-		tty_insert_flip_string_fixed_flag(tty, data, tty_flag,
+		tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag,
 							urb->actual_length);
 	}