drm: Small logic fix in drm_mode_setcrtc

Match the logic to the comments in the debug message
Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -1461,7 +1461,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 		goto out;
 	}
 
-	if (crtc_req->count_connectors > 0 && !mode && !fb) {
+	if (crtc_req->count_connectors > 0 && (!mode || !fb)) {
 		DRM_DEBUG("Count connectors is %d but no mode or fb set\n",
 			  crtc_req->count_connectors);
 		ret = -EINVAL;