serial: 8250: Document termios parameter of serial8250_em485_config()

With W=1:

    drivers/tty/serial/8250/8250_port.c:679: warning: Function parameter or member 'termios' not described in 'serial8250_em485_config'

Fix this by documenting the parameter.

Fixes: ae50bb27 ("serial: take termios_rwsem for ->rs485_config() & pass termios as param")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/2bd1e62be1d5d33333002910372feecc6d52e78f.1682071013.git.geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -669,6 +669,7 @@ EXPORT_SYMBOL_GPL(serial8250_em485_supported);
 /**
  * serial8250_em485_config() - generic ->rs485_config() callback
  * @port: uart port
+ * @termios: termios structure
  * @rs485: rs485 settings
  *
  * Generic callback usable by 8250 uart drivers to activate rs485 settings