drm: correct comments

On failure, these functions return error pointer, not NULL.
Signed-off-by: Liu Zixian <liuzixian4@huawei.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220718015357.1722-1-liuzixian4@huawei.com

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -662,7 +662,7 @@ EXPORT_SYMBOL(drm_gem_shmem_print_info);
  * drm_gem_shmem_get_pages_sgt() instead.
  *
  * Returns:
- * A pointer to the scatter/gather table of pinned pages or NULL on failure.
+ * A pointer to the scatter/gather table of pinned pages or error pointer on failure.
  */
 struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem)
 {

include/drm/drm_gem_shmem_helper.h

@@ -210,7 +210,7 @@ static inline void drm_gem_shmem_object_unpin(struct drm_gem_object *obj)
  * use it as their &drm_gem_object_funcs.get_sg_table handler.
  *
  * Returns:
- * A pointer to the scatter/gather table of pinned pages or NULL on failure.
+ * A pointer to the scatter/gather table of pinned pages or error pointer on failure.
  */
 static inline struct sg_table *drm_gem_shmem_object_get_sg_table(struct drm_gem_object *obj)
 {