serial: stm32: update conflicting RTS/CTS config comment

The comment for conflicting RTS/CTS config refers to "st, hw-flow-ctrl",
but this property is deprecated since the generic RTS/CTS property has
been introduced by the patch 'serial: stm32: Use generic DT binding for
announcing RTS/CTS lines'.
Update the comment to refer to both generic and deprecated RTS/CTS
properties.
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210106162203.28854-7-erwan.leray@foss.st.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1031,7 +1031,10 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 		goto err_clk;
 	}
 
-	/* Both CTS/RTS gpios and "st,hw-flow-ctrl" should not be specified */
+	/*
+	 * Both CTS/RTS gpios and "st,hw-flow-ctrl" (deprecated) or "uart-has-rtscts"
+	 * properties should not be specified.
+	 */
 	if (stm32port->hw_flow_control) {
 		if (mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_CTS) ||
 		    mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_RTS)) {