drm/exynos: clean up description of exynos_drm_crtc

This patch removes unnecessary descriptions on
exynos_drm_crtc structure and adds one description
which specifies what pipe_clk member does.

pipe_clk support had been added by below patch without any description,
	 drm/exynos: add support for pipeline clock to the framework
		Commit-id : f26b9343Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_drv.h

@@ -160,12 +160,9 @@ struct exynos_drm_clk {
  *	drm framework doesn't support multiple irq yet.
  *	we can refer to the crtc to current hardware interrupt occurred through
  *	this pipe value.
- * @enabled: if the crtc is enabled or not
- * @event: vblank event that is currently queued for flip
- * @wait_update: wait all pending planes updates to finish
- * @pending_update: number of pending plane updates in this crtc
  * @ops: pointer to callbacks for exynos drm specific functionality
  * @ctx: A pointer to the crtc's implementation specific context
+ * @pipe_clk: A pointer to the crtc's pipeline clock.
  */
 struct exynos_drm_crtc {
 	struct drm_crtc			base;