drm: fix memory leak around mode_group (v2)

This mode group id_list was never being freed.

v2: take David's suggestion to free in minor_free.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -1378,6 +1378,12 @@ static int drm_mode_group_init(struct drm_device *dev, struct drm_mode_group *gr
 	return 0;
 }
 
+void drm_mode_group_destroy(struct drm_mode_group *group)
+{
+	kfree(group->id_list);
+	group->id_list = NULL;
+}
+
 /*
  * NOTE: Driver's shouldn't ever call drm_mode_group_init_legacy_group - it is
  * the drm core's responsibility to set up mode control groups.

drivers/gpu/drm/drm_stub.c

@@ -294,6 +294,7 @@ static void drm_minor_free(struct drm_device *dev, unsigned int type)
 
 	slot = drm_minor_get_slot(dev, type);
 	if (*slot) {
+		drm_mode_group_destroy(&(*slot)->mode_group);
 		kfree(*slot);
 		*slot = NULL;
 	}

include/drm/drm_crtc.h

@@ -915,6 +915,7 @@ extern const char *drm_get_tv_subconnector_name(int val);
 extern const char *drm_get_tv_select_name(int val);
 extern void drm_fb_release(struct drm_file *file_priv);
 extern int drm_mode_group_init_legacy_group(struct drm_device *dev, struct drm_mode_group *group);
+extern void drm_mode_group_destroy(struct drm_mode_group *group);
 extern bool drm_probe_ddc(struct i2c_adapter *adapter);
 extern struct edid *drm_get_edid(struct drm_connector *connector,
 				 struct i2c_adapter *adapter);