tty: serial: 8250: Cleanup p->em485 in serial8250_unregister_port

Formally, currently there is no memory leak, but if
serial8250_ports[line] is reused with other 8250 driver, then em485
will be already activated and it will cause issues.

Fixes: e490c914 ("tty: Add software emulated RS485 support for 8250")
Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_core.c

@@ -1074,6 +1074,15 @@ void serial8250_unregister_port(int line)
 	struct uart_8250_port *uart = &serial8250_ports[line];
 
 	mutex_lock(&serial_mutex);
+
+	if (uart->em485) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&uart->port.lock, flags);
+		serial8250_em485_destroy(uart);
+		spin_unlock_irqrestore(&uart->port.lock, flags);
+	}
+
 	uart_remove_one_port(&serial8250_reg, &uart->port);
 	if (serial8250_isa_devs) {
 		uart->port.flags &= ~UPF_BOOT_AUTOCONF;