drm: Mark constant arrays of drm_display_mode const

... and fixup some methods to accept the constant argument.

Now that constant module arrays are loaded into read-only memory, using
const appropriately has some benefits beyond warning the programmer
about likely mistakes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 58e65f9..25bf873 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -593,7 +593,7 @@
  *
  * Return @modes's hsync rate in kHz, rounded to the nearest int.
  */
-int drm_mode_hsync(struct drm_display_mode *mode)
+int drm_mode_hsync(const struct drm_display_mode *mode)
 {
 	unsigned int calc_val;
 
@@ -627,7 +627,7 @@
  * If it is 70.288, it will return 70Hz.
  * If it is 59.6, it will return 60Hz.
  */
-int drm_mode_vrefresh(struct drm_display_mode *mode)
+int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
 	int refresh = 0;
 	unsigned int calc_val;
@@ -725,7 +725,7 @@
  * a pointer to it.  Used to create new instances of established modes.
  */
 struct drm_display_mode *drm_mode_duplicate(struct drm_device *dev,
-					    struct drm_display_mode *mode)
+					    const struct drm_display_mode *mode)
 {
 	struct drm_display_mode *nmode;
 	int new_id;