ASoc: wm8900: Drop empty spi_driver remove callback

A driver with a remove callback that just returns 0 behaves identically
to a driver with no remove callback at all. So simplify accordingly.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20211020125726.22946-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Mark Brown <broonie@kernel.org>