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: 26291c54e111ff6ba87a164d85d4a4e134b7315c

diff --cc MAINTAINERS
Simple merge

diff --cc drivers/spi/spi.c
Simple merge

diff --cc drivers/spi/spidev.c
Simple merge

diff --cc include/linux/spi/spi.h
Simple merge