Set the ->num_chipselect field in struct cqspi_st and struct
spi_controller to the current number of chip-select. The value is
dependent on declared flashes in devicetree.

Previously, the num-cs property from devicetree or the maximum value was
being reported.
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://msgid.link/r/20240209-cdns-qspi-cs-v1-3-a4f9dfed9ab4@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>