t7401: squelch garbage output

The script had an unconditional output done outside of test_expect_*
construct, which leaked out and contaminated the output without -v.
Squelch it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7401-submodule-summary.sh

diff --git a/t/t7401-submodule-summary.sh b/t/t7401-submodule-summary.sh
index 0f3c42a..b9a2219 100755
--- a/t/t7401-submodule-summary.sh
+++ b/t/t7401-submodule-summary.sh
@@ -30,7 +30,7 @@
 }
 
 test_create_repo sm1 &&
-add_file . foo
+add_file . foo >/dev/null
 
 head1=$(add_file sm1 foo1 foo2)