Other delay values follow the delay-ns naming convention, so unify the
newly introduced spi-cs-setup-ns property for consistency.

Also fix a typo while we're here.

Fixes: f6c911f3 ("spi: dt-bindings: Introduce spi-cs-setup-ns property")
Signed-off-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230104093631.15611-2-marcan@marcan.stSigned-off-by: Mark Brown <broonie@kernel.org>