mfd: Remove redundant spi driver bus initialization

In ancient times it was necessary to manually initialize the bus field of an
spi_driver to spi_bus_type. These days this is done in spi_driver_register(),
so we can drop the manual assignment.

The patch was generated using the following coccinelle semantic patch:
// <smpl>
@@
identifier _driver;
@@
struct spi_driver _driver = {
	.driver = {
-		.bus = &spi_bus_type,
	},
};
// </smpl>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/mc13xxx-core.c

@@ -805,7 +805,6 @@ static struct spi_driver mc13xxx_driver = {
 	.id_table = mc13xxx_device_id,
 	.driver = {
 		.name = "mc13xxx",
-		.bus = &spi_bus_type,
 		.owner = THIS_MODULE,
 	},
 	.probe = mc13xxx_probe,

drivers/mfd/tps65912-spi.c

@@ -111,7 +111,6 @@ static int __devexit tps65912_spi_remove(struct spi_device *spi)
 static struct spi_driver tps65912_spi_driver = {
 	.driver = {
 		.name = "tps65912",
-		.bus = &spi_bus_type,
 		.owner = THIS_MODULE,
 	},
 	.probe	= tps65912_spi_probe,

drivers/mfd/wm831x-spi.c

@@ -94,7 +94,6 @@ MODULE_DEVICE_TABLE(spi, wm831x_spi_id);
 static struct spi_driver wm831x_spi_driver = {
 	.driver = {
 		.name	= "wm831x",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 		.pm	= &wm831x_spi_pm,
 	},