tests: Replace 'suite' with 'tenv'

Change-Id: I777ec59ffd83b861ddc09e85e52d7a8896264b8c
diff --git a/sysmocom/suites/voice/mo_mt_call.py b/sysmocom/suites/voice/mo_mt_call.py
index 740b1fe..2a2afa4 100755
--- a/sysmocom/suites/voice/mo_mt_call.py
+++ b/sysmocom/suites/voice/mo_mt_call.py
@@ -2,7 +2,7 @@
 from osmo_gsm_tester.testenv import *
 
 import testlib
-suite.test_import_modules_register_for_cleanup(testlib)
+tenv.test_import_modules_register_for_cleanup(testlib)
 from testlib import test_mo_mt_call
 
 test_mo_mt_call(False, False)