spi: zynq-qspi: Anything else than CS0 is not supported yet

Unlike what the driver is currently advertizing, CS0 only can be used,
CS1 is not supported at all. Prevent people to use CS1.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20191108140744.1734-2-miquel.raynal@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-zynq-qspi.c

@@ -680,10 +680,14 @@ static int zynq_qspi_probe(struct platform_device *pdev)
 
 	ret = of_property_read_u32(np, "num-cs",
 				   &num_cs);
-	if (ret < 0)
+	if (ret < 0) {
 		ctlr->num_chipselect = ZYNQ_QSPI_DEFAULT_NUM_CS;
-	else
+	} else if (num_cs > ZYNQ_QSPI_DEFAULT_NUM_CS) {
+		dev_err(&pdev->dev, "anything but CS0 is not yet supported\n");
+		goto remove_master;
+	} else {
 		ctlr->num_chipselect = num_cs;
+	}
 
 	ctlr->mode_bits =  SPI_RX_DUAL | SPI_RX_QUAD |
 			    SPI_TX_DUAL | SPI_TX_QUAD;