Avoid TREBLE_TESTING_OVERRIDE

This is moved from an environmental variable to a function since
getenv is problematic in multi-threaded testing environments.

Bug: 156668058
Test: fmq_test
Change-Id: I54c6a973ef9d1cec98330268ed0a40c2564ee42c
diff --git a/tests/msgq/1.0/default/mq_test_service.cpp b/tests/msgq/1.0/default/mq_test_service.cpp
index b5cb662..b921bfd 100644
--- a/tests/msgq/1.0/default/mq_test_service.cpp
+++ b/tests/msgq/1.0/default/mq_test_service.cpp
@@ -24,5 +24,6 @@
 using android::hardware::defaultPassthroughServiceImplementation;
 
 int main() {
+    android::hardware::details::setTrebleTestingOverride(true);
     return defaultPassthroughServiceImplementation<ITestMsgQ>();
 }