spi: spi-fsl-dspi: Use max_native_cs instead of num_chipselect to set SPI_MCR

If cs-gpios property is used in devicetree then ctlr->num_chipselect value
may be changed by spi_get_gpio_descs().
So use ctlr->max_native_cs instead of ctlr->num_chipselect to set SPI_MCR

Fixes: 4fcc7c22 (spi: spi-fsl-dspi: Don't access reserved fields in SPI_MCR)
Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
Link: https://lore.kernel.org/r/20201201085916.63543-1-fido_max@inbox.ruSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -1165,7 +1165,7 @@ static int dspi_init(struct fsl_dspi *dspi)
 	unsigned int mcr;
 
 	/* Set idle states for all chip select signals to high */
-	mcr = SPI_MCR_PCSIS(GENMASK(dspi->ctlr->num_chipselect - 1, 0));
+	mcr = SPI_MCR_PCSIS(GENMASK(dspi->ctlr->max_native_cs - 1, 0));
 
 	if (dspi->devtype_data->trans_mode == DSPI_XSPI_MODE)
 		mcr |= SPI_MCR_XSPI;
@@ -1250,7 +1250,7 @@ static int dspi_probe(struct platform_device *pdev)
 
 	pdata = dev_get_platdata(&pdev->dev);
 	if (pdata) {
-		ctlr->num_chipselect = pdata->cs_num;
+		ctlr->num_chipselect = ctlr->max_native_cs = pdata->cs_num;
 		ctlr->bus_num = pdata->bus_num;
 
 		/* Only Coldfire uses platform data */
@@ -1263,7 +1263,7 @@ static int dspi_probe(struct platform_device *pdev)
 			dev_err(&pdev->dev, "can't get spi-num-chipselects\n");
 			goto out_ctlr_put;
 		}
-		ctlr->num_chipselect = cs_num;
+		ctlr->num_chipselect = ctlr->max_native_cs = cs_num;
 
 		of_property_read_u32(np, "bus-num", &bus_num);
 		ctlr->bus_num = bus_num;