spi: make remove callback a void function

Merge series from Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:

this series goal is to change the spi remove callback's return value to void.
After numerous patches nearly all drivers already return 0 unconditionally.
The four first patches in this series convert the remaining three drivers to
return 0, the final patch changes the remove prototype and converts all
implementers.

base-commit: 26291c54e1

include/linux/spi/spi.h

@@ -281,7 +281,7 @@ struct spi_message;
 struct spi_driver {
 	const struct spi_device_id *id_table;
 	int			(*probe)(struct spi_device *spi);
-	int			(*remove)(struct spi_device *spi);
+	void			(*remove)(struct spi_device *spi);
 	void			(*shutdown)(struct spi_device *spi);
 	struct device_driver	driver;
 };