spi: reduce device chip select limit again

spi: reduce device chip select limit again

The spi chipselect limit SPI_CS_CNT_MAX was raised with commit
2f8c7c3715f2 ("spi: Raise limit on number of chip selects") from 4 to 16
to accommodate spi controllers with more than 4 chip selects, and then
later to 24 with commit 96893cdd4760 ("spi: Raise limit on number of
chip selects to 24").

Now that we removed SPI_CS_CNT_MAX limiting the chip selects of
controllers, we can reduce the amount of chip selects per device again
to 4, the original value.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://patch.msgid.link/20250915183725.219473-7-jonas.gorski@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>