spi: spi-fsl-lpspi: Remove num_cs from device struct

This is only used during probe() call, so there is no need to store it
longer than that.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Link: https://lore.kernel.org/r/20230705090145.1354663-1-alexander.stein@ew.tq-group.com


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