spi: cadence-qspi: assert each subnode flash CS is valid

Check each flash CS against the num-cs property from devicetree.
Fallback to the driver max supported value (CQSPI_MAX_CHIPSELECT) if
num-cs isn't present.

cqspi->num_chipselect is set in cqspi_of_get_pdata() to the num-cs
devicetree property, or to CQSPI_MAX_CHIPSELECT if num-cs is not set.
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Link: https://msgid.link/r/20240209-cdns-qspi-cs-v1-1-a4f9dfed9ab4@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-cadence-quadspi.c

@@ -1635,7 +1635,7 @@ static int cqspi_setup_flash(struct cqspi_st *cqspi)
 			return ret;
 		}
 
-		if (cs >= CQSPI_MAX_CHIPSELECT) {
+		if (cs >= cqspi->num_chipselect) {
 			dev_err(dev, "Chip select %d out of range.\n", cs);
 			of_node_put(np);
 			return -EINVAL;