ARM: imx: Fix boot crash if ocotp is not found

The imx_soc_device_init functions tries to fetch the ocotp regmap in
order to soc serial number. If regmap fetch fails then a message is
printed but regmap_read is called anyway and the system crashes.

Failing to lookup ocotp regmap shouldn't be a fatal boot error so check
that the pointer is valid.

Only side-effect of ocotp lookup failure now is that serial number will
be reported as all-zeros which is acceptable.

Cc: stable@vger.kernel.org
Fixes: 8267ff89 ("ARM: imx: Add serial number support for i.MX6/7 SoCs")
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Tested-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/cpu.c

@@ -84,7 +84,7 @@ struct device * __init imx_soc_device_init(void)
 	const char *ocotp_compat = NULL;
 	struct soc_device *soc_dev;
 	struct device_node *root;
-	struct regmap *ocotp;
+	struct regmap *ocotp = NULL;
 	const char *soc_id;
 	u64 soc_uid = 0;
 	u32 val;
@@ -175,7 +175,9 @@ struct device * __init imx_soc_device_init(void)
 		ocotp = syscon_regmap_lookup_by_compatible(ocotp_compat);
 		if (IS_ERR(ocotp))
 			pr_err("%s: failed to find %s regmap!\n", __func__, ocotp_compat);
+	}
 
+	if (!IS_ERR_OR_NULL(ocotp)) {
 		regmap_read(ocotp, OCOTP_UID_H, &val);
 		soc_uid = val;
 		regmap_read(ocotp, OCOTP_UID_L, &val);