drm: fix kernel-doc warnings in drm_crtc.h

Fix the following 'make htmldocs' warning:

  .//include/drm/drm_crtc.h:929: warning: Excess struct/union/enum/typedef member 'base' description in 'drm_bridge'
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_crtc.h

@@ -911,7 +911,6 @@ struct drm_bridge_funcs {
  * @next: the next bridge in the encoder chain
  * @of_node: device node pointer to the bridge
  * @list: to keep track of all added bridges
- * @base: base mode object
  * @funcs: control functions
  * @driver_private: pointer to the bridge driver's internal context
  */