drd/tests/pth_once: Restrict the number of callers to three.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11938 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/drd/tests/pth_once.vgtest b/drd/tests/pth_once.vgtest
index 338b5fc..232fd73 100644
--- a/drd/tests/pth_once.vgtest
+++ b/drd/tests/pth_once.vgtest
@@ -1,5 +1,5 @@
 prereq: test -e tsan_unittest && ./supported_libpthread
-vgopts: --read-var-info=yes --check-stack-var=yes
+vgopts: --read-var-info=yes --check-stack-var=yes --num-callers=3
 prog: tsan_unittest
 args: 106
 stderr_filter: filter_error_summary