serial: 8250: Discard RTS/DTS setting from clock update method

It has been a mistake to add the MCR register RTS/DTS fields setting in
the generic method of the UART reference clock update. There is no point
in asserting these lines at that procedure. Just discard the
serial8250_out_MCR() mathod invocation from there then.

Fixes: 868f3ee6 ("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/20200923161950.6237-2-Sergey.Semin@baikalelectronics.ruSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -2665,7 +2665,6 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk)
 
 	serial8250_set_divisor(port, baud, quot, frac);
 	serial_port_out(port, UART_LCR, up->lcr);
-	serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS);
 
 	spin_unlock_irqrestore(&port->lock, flags);
 	serial8250_rpm_put(up);