vts: fix TryDifferentGovernors in Power hal test

The test should return when it cannot open cpu governor files
BUG: 62138092

Test: build sdk_gphone_x86-userdebug, launch emulator,
run test: run vts -m VtsHalPowerV1_0Target
The test should all pass.

Change-Id: I3b47261e9525b6a04e995dac1ad63d9cc088b004

power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp

@@ -77,6 +77,7 @@ TEST_F(PowerHidlTest, TryDifferentGovernors) {
   if (fd1 < 0 || fd2 < 0) {
     // Files don't exist, so skip the rest of the test case
     SUCCEED();
+    return;
   }
 
   char old_governor[80];