serial: ar933x: Deassert Transmit Enable on ->rs485_config()

The ar933x_uart driver neglects to deassert Transmit Enable when
->rs485_config() is invoked.  Fix it.

Fixes: 9be1064f ("serial: ar933x_uart: add RS485 support")
Cc: stable@vger.kernel.org # v5.7+
Cc: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/5b36af26e57553f084334666e7d24c7fd131a01e.1662887231.git.lukas@wunner.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/ar933x_uart.c

@@ -583,6 +583,13 @@ static const struct uart_ops ar933x_uart_ops = {
 static int ar933x_config_rs485(struct uart_port *port, struct ktermios *termios,
 				struct serial_rs485 *rs485conf)
 {
+	struct ar933x_uart_port *up =
+			container_of(port, struct ar933x_uart_port, port);
+
+	if (port->rs485.flags & SER_RS485_ENABLED)
+		gpiod_set_value(up->rts_gpiod,
+			!!(rs485conf->flags & SER_RS485_RTS_AFTER_SEND));
+
 	return 0;
 }