media: v4l: fwnode: Make v4l2_fwnode_endpoint_free() safer

Assign vep->link_frequencies to NULL after releasing its memory. Without
this change, multiple calls to v4l2_fwnode_endpoint_free() would result in
double kfree calls.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/v4l2-core/v4l2-fwnode.c

@@ -512,6 +512,7 @@ void v4l2_fwnode_endpoint_free(struct v4l2_fwnode_endpoint *vep)
 		return;
 
 	kfree(vep->link_frequencies);
+	vep->link_frequencies = NULL;
 }
 EXPORT_SYMBOL_GPL(v4l2_fwnode_endpoint_free);