USB: serial: console: add support for flow control

Add support for enabling hardware flow control using the 'r' command
line option.

This also avoids a W=1 (-Wunused-but-set-variable) warning.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/console.c

@@ -102,6 +102,9 @@ static int usb_console_setup(struct console *co, char *options)
 		break;
 	}
 
+	if (doflow)
+		cflag |= CRTSCTS;
+
 	/*
 	 * no need to check the index here: if the index is wrong, console
 	 * code won't call us