spi: Rename spi-cs-setup-ns property to spi-cs-setup-delay-ns

As mentioned in the corresponding DT binding commit, the naming scheme
for delay properties includes "delay" in the name, so let's keep that
consistent.

Fixes: 33a2fde5

 ("spi: Introduce spi-cs-setup-ns property")
Signed-off-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230104093631.15611-3-marcan@marcan.st
Signed-off-by: Mark Brown <broonie@kernel.org>