build: let touch on directory as last step

We need to let these instructions in kmod to be the last executed ones.
Otherwise the subdirectory containing the modules could propagate up the
time access.
diff --git a/Makefile.am b/Makefile.am
index 7774759..a99a5a2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -215,10 +215,10 @@
 ROOTFS_PRISTINE = $(top_srcdir)/testsuite/rootfs-pristine
 CREATE_ROOTFS = $(AM_V_GEN) ( $(RM) -rf $(ROOTFS) && mkdir -p $(dir $(ROOTFS)) && \
 				cp -r $(ROOTFS_PRISTINE) $(ROOTFS) && \
-				touch testsuite/stamp-rootfs && \
 				find $(ROOTFS) -type d -exec chmod +w {} \; && \
 				$(top_srcdir)/testsuite/populate-modules.sh \
-					$(MODULE_PLAYGROUND) $(ROOTFS) )
+					$(MODULE_PLAYGROUND) $(ROOTFS) ) && \
+				touch testsuite/stamp-rootfs
 
 build-module-playground:
 	$(AM_V_GEN)if test "$(top_srcdir)" != "$(top_builddir)"; then \