spi: fsl: fix use of spisel_boot signal on MPC8309

Commit 0f0581b24b ("spi: fsl: Convert to use CS GPIO descriptors")
broke the use of the SPISEL_BOOT signal as a chip select on the
MPC8309.

pdata->max_chipselect, which becomes master->num_chipselect, must be
initialized to take into account the possibility that there's one more
chip select in use than the number of GPIO chip selects.

Cc: stable@vger.kernel.org # v5.4+
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Linus Walleij <linus.walleij@linaro.org>
Fixes: 0f0581b24b ("spi: fsl: Convert to use CS GPIO descriptors")
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Link: https://lore.kernel.org/r/20201127152947.376-1-rasmus.villemoes@prevas.dk
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-spi.c

@@ -716,10 +716,11 @@ static int of_fsl_spi_probe(struct platform_device *ofdev)
 	type = fsl_spi_get_type(&ofdev->dev);
 	if (type == TYPE_FSL) {
 		struct fsl_spi_platform_data *pdata = dev_get_platdata(dev);
+		bool spisel_boot = false;
 #if IS_ENABLED(CONFIG_FSL_SOC)
 		struct mpc8xxx_spi_probe_info *pinfo = to_of_pinfo(pdata);
-		bool spisel_boot = of_property_read_bool(np, "fsl,spisel_boot");
 
+		spisel_boot = of_property_read_bool(np, "fsl,spisel_boot");
 		if (spisel_boot) {
 			pinfo->immr_spi_cs = ioremap(get_immrbase() + IMMR_SPI_CS_OFFSET, 4);
 			if (!pinfo->immr_spi_cs)
@@ -734,10 +735,14 @@ static int of_fsl_spi_probe(struct platform_device *ofdev)
 		 * supported on the GRLIB variant.
 		 */
 		ret = gpiod_count(dev, "cs");
-		if (ret <= 0)
+		if (ret < 0)
+			ret = 0;
+		if (ret == 0 && !spisel_boot) {
 			pdata->max_chipselect = 1;
-		else
+		} else {
+			pdata->max_chipselect = ret + spisel_boot;
 			pdata->cs_control = fsl_spi_cs_control;
+		}
 	}
 
 	ret = of_address_to_resource(np, 0, &mem);