drm/i915: Make disable_cursor_plane similar to commit_cursor_plane.

Update cursor_addr when disable_plane is called.
This is required to make commit_cursor_plane take a
crtc_state and a plane_state.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452164052-21752-5-git-send-email-maarten.lankhorst@linux.intel.comReviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -14256,6 +14256,9 @@ static void
 intel_disable_cursor_plane(struct drm_plane *plane,
 			   struct drm_crtc *crtc)
 {
+	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+
+	intel_crtc->cursor_addr = 0;
 	intel_crtc_update_cursor(crtc, false);
 }