of: constify property name parameters for helper functions

The helper functions for reading u32 integers, u32 arrays and strings
should have the property name as a const pointer.

Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/of/base.c b/drivers/of/base.c
index 02ed367..3ff22e3 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -610,8 +610,9 @@
  *
  * The out_value is modified only if a valid u32 value can be decoded.
  */
-int of_property_read_u32_array(const struct device_node *np, char *propname,
-			       u32 *out_values, size_t sz)
+int of_property_read_u32_array(const struct device_node *np,
+			       const char *propname, u32 *out_values,
+			       size_t sz)
 {
 	struct property *prop = of_find_property(np, propname, NULL);
 	const __be32 *val;
@@ -645,7 +646,7 @@
  *
  * The out_string pointer is modified only if a valid string can be decoded.
  */
-int of_property_read_string(struct device_node *np, char *propname,
+int of_property_read_string(struct device_node *np, const char *propname,
 				const char **out_string)
 {
 	struct property *prop = of_find_property(np, propname, NULL);