drivers/rtc/: 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 <[e-mail]>
Cc: John Stultz <[e-mail]>
Cc: Alessandro Zummo <[e-mail]>
Cc: Grant Likely <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/rtc/rtc-m41t93.c

···
 static struct spi_driver m41t93_driver = {
 	.driver = {
 		.name	= "rtc-m41t93",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 	},
 	.probe	= m41t93_probe,

drivers/rtc/rtc-m41t94.c

···
 static struct spi_driver m41t94_driver = {
 	.driver = {
 		.name	= "rtc-m41t94",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 	},
 	.probe	= m41t94_probe,

drivers/rtc/rtc-max6902.c

···
 static struct spi_driver max6902_driver = {
 	.driver = {
 		.name	= "rtc-max6902",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 	},
 	.probe	= max6902_probe,

drivers/rtc/rtc-pcf2123.c

···
 static struct spi_driver pcf2123_driver = {
 	.driver	= {
 			.name	= "rtc-pcf2123",
-			.bus	= &spi_bus_type,
 			.owner	= THIS_MODULE,
 	},
 	.probe	= pcf2123_probe,

drivers/rtc/rtc-rs5c348.c

···
 static struct spi_driver rs5c348_driver = {
 	.driver = {
 		.name	= "rtc-rs5c348",
-		.bus	= &spi_bus_type,
 		.owner	= THIS_MODULE,
 	},
 	.probe	= rs5c348_probe,