spi/imx: prevent NULL pointer dereference in spi_imx_probe()

When no platform_data is present and either 'spi-num-chipselects' is
not defined in the DT or 'cs-gpios' has less entries than
'spi-num-chipselects' specifies, the NULL platform_data pointer is
being dereferenced.
Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi-imx.c

@@ -766,8 +766,12 @@ static int __devinit spi_imx_probe(struct platform_device *pdev)
 	}
 
 	ret = of_property_read_u32(np, "fsl,spi-num-chipselects", &num_cs);
-	if (ret < 0)
-		num_cs = mxc_platform_info->num_chipselect;
+	if (ret < 0) {
+		if (mxc_platform_info)
+			num_cs = mxc_platform_info->num_chipselect;
+		else
+			return ret;
+	}
 
 	master = spi_alloc_master(&pdev->dev,
 			sizeof(struct spi_imx_data) + sizeof(int) * num_cs);
@@ -784,7 +788,7 @@ static int __devinit spi_imx_probe(struct platform_device *pdev)
 
 	for (i = 0; i < master->num_chipselect; i++) {
 		int cs_gpio = of_get_named_gpio(np, "cs-gpios", i);
-		if (cs_gpio < 0)
+		if (cs_gpio < 0 && mxc_platform_info)
 			cs_gpio = mxc_platform_info->chipselect[i];
 
 		spi_imx->chipselect[i] = cs_gpio;