drm/syncobj: Mark local add/remove callback functions as static

drivers/gpu/drm/drm_syncobj.c:181:6: warning: no previous prototype for ‘drm_syncobj_add_callback’ [-Wmissing-prototypes]
drivers/gpu/drm/drm_syncobj.c:190:6: warning: no previous prototype for ‘drm_syncobj_remove_callback’ [-Wmissing-prototypes]

Fixing that leads to

drivers/gpu/drm/drm_syncobj.c:181:13: warning: ‘drm_syncobj_add_callback’ defined but not used [-Wunused-function]

so remove the unused drm_syncobj_add_callback() entirely.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20181031120710.21582-1-chris@chris-wilson.co.ukReviewed-by: Chunming Zhou <david1.zhou@amd.com>

drivers/gpu/drm/drm_syncobj.c

@@ -123,8 +123,8 @@ struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
 }
 EXPORT_SYMBOL(drm_syncobj_find);
 
-static struct dma_fence
-*drm_syncobj_find_signal_pt_for_point(struct drm_syncobj *syncobj,
+static struct dma_fence *
+drm_syncobj_find_signal_pt_for_point(struct drm_syncobj *syncobj,
 				     uint64_t point)
 {
 	struct drm_syncobj_signal_pt *signal_pt;
@@ -178,16 +178,7 @@ static void drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
 	mutex_unlock(&syncobj->cb_mutex);
 }
 
-void drm_syncobj_add_callback(struct drm_syncobj *syncobj,
-			      struct drm_syncobj_cb *cb,
-			      drm_syncobj_func_t func)
-{
-	mutex_lock(&syncobj->cb_mutex);
-	drm_syncobj_add_callback_locked(syncobj, cb, func);
-	mutex_unlock(&syncobj->cb_mutex);
-}
-
-void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
+static void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
 					struct drm_syncobj_cb *cb)
 {
 	mutex_lock(&syncobj->cb_mutex);