ASoC: Implement SPI device unregistration for WM8731

Completely untested.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8731.c

@@ -655,12 +655,17 @@ static int __devinit wm8731_spi_probe(struct spi_device *spi)
 	codec->hw_write = (hw_write_t)wm8731_spi_write;
 	codec->dev = &spi->dev;
 
+	spi->dev.driver_data = wm8731;
+
 	return wm8731_register(wm8731);
 }
 
 static int __devexit wm8731_spi_remove(struct spi_device *spi)
 {
-	/* FIXME: This isn't actually implemented... */
+	struct wm8731_priv *wm8731 = spi->dev.driver_data;
+
+	wm8731_unregister(wm8731);
+
 	return 0;
 }