spidev: Add "spidev" compatible string to silence warning

See: raspberrypi/linux#1054

Author: Phil Elwell

drivers/spi/spidev.c

@@ -677,6 +677,7 @@ static const struct of_device_id spidev_dt_ids[] = {
 	{ .compatible = "lineartechnology,ltc2488" },
 	{ .compatible = "ge,achc" },
 	{ .compatible = "semtech,sx1301" },
+	{ .compatible = "spidev" },
 	{},
 };
 MODULE_DEVICE_TABLE(of, spidev_dt_ids);