src/worker_collection/worker_tree.c: add missing include

src/worker_collection/worker_tree.c

@@ -20,7 +20,7 @@
 #ifdef STARPU_HAVE_HWLOC
 #include <hwloc.h>
 /* #include "tree.h" */
-/* #include "core/workers.h" */
+#include "core/workers.h"
 
 static unsigned tree_has_next(struct starpu_worker_collection *workers, struct starpu_sched_ctx_iterator *it)
 {