tmpfiles: fix build
After I merged #12750 we don't build anymore, since the merged PR (which
passed CI) uses prefix_root() which doesn't exist anymore. Let's fix
that.
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index 02eecf3..b968d83 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -2625,7 +2625,7 @@
} else if (arg_root) {
char *p;
- p = prefix_root(arg_root, i.argument);
+ p = path_join(arg_root, i.argument);
if (!p)
return log_oom();
free_and_replace(i.argument, p);