video: display_timing: make parameter const

As the device_node pointer is not changed in of_get_display_timing and
parse_timing_property it can be a const pointer.
Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/video/of_display_timing.c

@@ -23,7 +23,7 @@
  * Every display_timing can be specified with either just the typical value or
  * a range consisting of min/typ/max. This function helps handling this
  **/
-static int parse_timing_property(struct device_node *np, const char *name,
+static int parse_timing_property(const struct device_node *np, const char *name,
 			  struct timing_entry *result)
 {
 	struct property *prop;
@@ -56,7 +56,8 @@ static int parse_timing_property(struct device_node *np, const char *name,
  * of_get_display_timing - parse display_timing entry from device_node
  * @np: device_node with the properties
  **/
-static struct display_timing *of_get_display_timing(struct device_node *np)
+static struct display_timing *of_get_display_timing(const struct device_node
+						    *np)
 {
 	struct display_timing *dt;
 	u32 val = 0;