media: vimc: fix start stream when link is disabled

If link is disabled, media_entity_remote_pad returns NULL, causing a
NULL pointer deference.
Ignore links that are not enabled instead.

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/vimc/vimc-common.c

@@ -276,6 +276,8 @@ int vimc_pipeline_s_stream(struct media_entity *ent, int enable)
 
 		/* Start the stream in the subdevice direct connected */
 		pad = media_entity_remote_pad(&ent->pads[i]);
+		if (!pad)
+			continue;
 
 		if (!is_media_entity_v4l2_subdev(pad->entity))
 			return -EINVAL;