avoid talloc abort in simtrace2 frontend_append_script_env()

talloc requires a valid context for the allocation, we cannot use
env[i] as context.

Change-Id: I82b5e6b91b39d6f5c2a7492adb8c6193083e0d70
diff --git a/src/client/user_simtrace2.c b/src/client/user_simtrace2.c
index 5d5bfc1..f84db9d 100644
--- a/src/client/user_simtrace2.c
+++ b/src/client/user_simtrace2.c
@@ -361,10 +361,9 @@
 	return 0;
 }
 
-int frontend_append_script_env(struct bankd_client *bc, char **env, size_t max_env)
+int frontend_append_script_env(struct bankd_client *bc, char **env, int i, size_t max_env)
 {
 	struct osmo_st2_cardem_inst *ci = bc->cardem;
-	int i = 0;
 
 	if (max_env < 4)
 		return -ENOSPC;