w1-gpio: fix unused variable warning

Commit 8a1861d997 ("w1-gpio: Simplify & get rid of defines") removed the
compile guards from the device-tree id table, thereby generating a
warning when building without device-tree support.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/masters/w1-gpio.c

@@ -47,11 +47,13 @@ static u8 w1_gpio_read_bit(void *data)
 	return gpio_get_value(pdata->pin) ? 1 : 0;
 }
 
+#if defined(CONFIG_OF)
 static struct of_device_id w1_gpio_dt_ids[] = {
 	{ .compatible = "w1-gpio" },
 	{}
 };
 MODULE_DEVICE_TABLE(of, w1_gpio_dt_ids);
+#endif
 
 static int w1_gpio_probe_dt(struct platform_device *pdev)
 {