regmap: fix NULL pointer dereference in regmap_get_val_endian

Recents commits for getting reg endianness causing NULL pointer
dereference if dev is passed NULL in regmap_init_mmio. This patch
fixes this issue, and allows to parse reg endianness only if dev
and dev->of_node exist.
Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -477,7 +477,7 @@ static enum regmap_endian regmap_get_val_endian(struct device *dev,
 					const struct regmap_bus *bus,
 					const struct regmap_config *config)
 {
-	struct device_node *np = dev->of_node;
+	struct device_node *np;
 	enum regmap_endian endian;
 
 	/* Retrieve the endianness specification from the regmap config */
@@ -487,6 +487,10 @@ static enum regmap_endian regmap_get_val_endian(struct device *dev,
 	if (endian != REGMAP_ENDIAN_DEFAULT)
 		return endian;
 
+	/* If the dev and dev->of_node exist try to get endianness from DT */
+	if (dev && dev->of_node) {
+		np = dev->of_node;
+
 		/* Parse the device's DT node for an endianness specification */
 		if (of_property_read_bool(np, "big-endian"))
 			endian = REGMAP_ENDIAN_BIG;
@@ -496,6 +500,7 @@ static enum regmap_endian regmap_get_val_endian(struct device *dev,
 		/* If the endianness was specified in DT, use that */
 		if (endian != REGMAP_ENDIAN_DEFAULT)
 			return endian;
+	}
 
 	/* Retrieve the endianness specification from the bus config */
 	if (bus && bus->val_format_endian_default)