vibrator: Report amplitude control capability

* Missed in d2f0a55ddb5d9d4693b184c3e6b14cb38eebad16

Change-Id: I82feecfccd93a0403fd7fb3baa2263880d4e3dac
diff --git a/aidl/vibrator/Vibrator.cpp b/aidl/vibrator/Vibrator.cpp
index 134ba4e..ebed1e4 100644
--- a/aidl/vibrator/Vibrator.cpp
+++ b/aidl/vibrator/Vibrator.cpp
@@ -39,6 +39,9 @@
 
     #ifdef VIBRATOR_SUPPORTS_EFFECTS
     *_aidl_return |= IVibrator::CAP_PERFORM_CALLBACK;
+
+    if (mVibratorStrengthSupported)
+        *_aidl_return |= IVibrator::CAP_AMPLITUDE_CONTROL;
     #endif
 
     return ndk::ScopedAStatus::ok();