spi: Convert to platform remove callback returning

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

This patch series adapts the platform drivers below drivers/spi
to use the .remove_new() callback. Compared to the traditional .remove()
callback .remove_new() returns no value. This is a good thing because
the driver core doesn't (and cannot) cope for errors during remove. The
only effect of a non-zero return value in .remove() is that the driver
core emits a warning. The device is removed anyhow and an early return
from .remove() usually yields a resource leak.

By changing the remove callback to return void driver authors cannot
reasonably assume any more that there is some kind of cleanup later.

All drivers touched here returned zero unconditionally in their remove
callback, so they could all be converted trivially to .remove_new().