ASoC: Remove unneeded use of spi_bus_type

No need to explicitly set the bus type, spi_register_driver does
that for us.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8728.c

@@ -307,7 +307,6 @@ static int __devexit wm8728_spi_remove(struct spi_device *spi)
 static struct spi_driver wm8728_spi_driver = {
 	.driver = {
 		.name	= "wm8728-codec",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 	},
 	.probe		= wm8728_spi_probe,