spi: Raise limit on number of chip selects to 24

We have a system which uses 24 SPI chip selects, raise the hard coded
limit accordingly.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://patch.msgid.link/20250629-spi-increase-number-of-cs-v2-1-85a0a09bab32@pengutronix.de


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