testsuite: fix du testsuite to not use changing directories

diff --git a/testsuite/du/du-l-works b/testsuite/du/du-l-works
index 61e9140..c3d2ec0 100644
--- a/testsuite/du/du-l-works
+++ b/testsuite/du/du-l-works
@@ -1,4 +1,4 @@
-[ -n "$d" ] || d=..
+d=/bin
 du -l "$d" > logfile.gnu
 busybox du -l "$d" > logfile.bb
 cmp logfile.gnu logfile.bb