vibrator: turn off vibrator after testing ChangeVibrationAmplitude

Turn off vibrator explicitly after testing ChangeVibrationAmplitude.

Bug: 232319176
Test: VtsHalVibratorTargetTest
Change-Id: I482ea8266378636340c614eda832f4237d22e005
diff --git a/vibrator/aidl/vts/VtsHalVibratorTargetTest.cpp b/vibrator/aidl/vts/VtsHalVibratorTargetTest.cpp
index 5251529..f8f3cbd 100644
--- a/vibrator/aidl/vts/VtsHalVibratorTargetTest.cpp
+++ b/vibrator/aidl/vts/VtsHalVibratorTargetTest.cpp
@@ -332,6 +332,7 @@
         sleep(1);
         EXPECT_EQ(Status::EX_NONE, vibrator->setAmplitude(1.0f).exceptionCode());
         sleep(1);
+        EXPECT_TRUE(vibrator->off().isOk());
     }
 }