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: NLars-Peter Clausen <lars@metafoo.de>
Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/mfd/da9052-spi.c

@@ -88,7 +88,6 @@ static struct spi_driver da9052_spi_driver = {
 	.id_table = da9052_spi_id,
 	.driver = {
 		.name = "da9052",
-		.bus = &spi_bus_type,
 		.owner = THIS_MODULE,
 	},
 };

drivers/mfd/stmpe-spi.c

@@ -122,7 +122,6 @@ MODULE_DEVICE_TABLE(spi, stmpe_id);
 static struct spi_driver stmpe_spi_driver = {
 	.driver = {
 		.name	= "stmpe-spi",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 #ifdef CONFIG_PM
 		.pm	= &stmpe_dev_pm_ops,