serial: 8250: Skip uninitialized TTY port baud rate update

It is erroneous to update the TTY port baud rate if it hasn't been
initialized yet, because in that case the TTY struct isn't set. So there
is no termios structure to get and re-calculate the baud if the current
baud can't be reached. Let's skip the baud rate update then until the port
is fully initialized.

Note the update UART clock method still sets the uartclk member with a new
ref clock value even if the port is turned off. The new UART ref clock
rate will be used later on the port starting up procedure.

Fixes: 868f3ee ("serial: 8250: Add 8250 port clock update method")
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200923161950.6237-3-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_port.c

@@ -2653,6 +2653,10 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk)
 		goto out_lock;
 
 	port->uartclk = uartclk;
+
+	if (!tty_port_initialized(&port->state->port))
+		goto out_lock;
+
 	termios = &port->state->port.tty->termios;
 
 	baud = serial8250_get_baud_rate(port, termios, NULL);