drm/nouveau/dispnv04: Use helper to turn off CRTC

Use shiny new drm_crtc_force_disable() instead of open coding the same.
No functional change intended.

Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/95bfab0175ea327f777d43dcc18034bf42ca2287.1465392124.git.lukas@wunner.de

drivers/gpu/drm/nouveau/dispnv04/tvnv17.c

@@ -749,13 +749,8 @@ static int nv17_tv_set_property(struct drm_encoder *encoder,
 
 		/* Disable the crtc to ensure a full modeset is
 		 * performed whenever it's turned on again. */
-		if (crtc) {
-			struct drm_mode_set modeset = {
-				.crtc = crtc,
-			};
-
-			drm_mode_set_config_internal(&modeset);
-		}
+		if (crtc)
+			drm_crtc_force_disable(crtc);
 	}
 
 	return 0;