spi: atmel-quadspi: Convert to platform remove

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

This series converts the atmel-quadspi driver to use the .remove_new()
callback that doesn't return an int but void. The motivation is to not
give driver authors a reason to (wrongly) believe that returning an
error code was sensible error handling. In fact the spi core only emits
a warning message in this case and otherwise continues as if the return
value was zero. This usually yields resource leaks that sometimes can
lead to exceptions later on.

The atmel-quadspi driver is one of these drivers that got error handling
wrong, this is fixed here and in the last patch the driver is converted
to .remove_new() with the eventual goal to change .remove() to return
void once all drivers are converted this way.