drm: Constify topology id

Make the topology id const since we don't want to change it.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200313162054.16009-2-ville.syrjala@linux.intel.comReviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/drm_connector.c

@@ -2392,7 +2392,7 @@ EXPORT_SYMBOL(drm_mode_put_tile_group);
  * tile group or NULL if not found.
  */
 struct drm_tile_group *drm_mode_get_tile_group(struct drm_device *dev,
-					       char topology[8])
+					       const char topology[8])
 {
 	struct drm_tile_group *tg;
 	int id;
@@ -2422,7 +2422,7 @@ EXPORT_SYMBOL(drm_mode_get_tile_group);
  * new tile group or NULL.
  */
 struct drm_tile_group *drm_mode_create_tile_group(struct drm_device *dev,
-						  char topology[8])
+						  const char topology[8])
 {
 	struct drm_tile_group *tg;
 	int ret;

include/drm/drm_connector.h

@@ -1617,9 +1617,9 @@ struct drm_tile_group {
 };
 
 struct drm_tile_group *drm_mode_create_tile_group(struct drm_device *dev,
-						  char topology[8]);
+						  const char topology[8]);
 struct drm_tile_group *drm_mode_get_tile_group(struct drm_device *dev,
-					       char topology[8]);
+					       const char topology[8]);
 void drm_mode_put_tile_group(struct drm_device *dev,
 			     struct drm_tile_group *tg);