Always specify underlying enum type.

Bug: 33197891
Test: compiles
Change-Id: I3d4822ea9a665708302d3bd1460425fddf1dcda9
diff --git a/audio/effect/2.0/IVisualizerEffect.hal b/audio/effect/2.0/IVisualizerEffect.hal
index 70dabf9..79dc9ee 100644
--- a/audio/effect/2.0/IVisualizerEffect.hal
+++ b/audio/effect/2.0/IVisualizerEffect.hal
@@ -20,7 +20,7 @@
 import IEffect;
 
 interface IVisualizerEffect extends IEffect {
-    enum CaptureSizeRange {
+    enum CaptureSizeRange : int32_t {
         MAX = 1024,  // maximum capture size in samples
         MIN = 128    // minimum capture size in samples
     };
@@ -35,7 +35,7 @@
      */
     getCaptureSize() generates (Result retval, uint16_t captureSize);
 
-    enum ScalingMode {
+    enum ScalingMode : int32_t {
         // Keep in sync with SCALING_MODE_... in
         // frameworks/base/media/java/android/media/audiofx/Visualizer.java
         NORMALIZED = 0,
@@ -62,7 +62,7 @@
      */
     getLatency() generates (Result retval, uint32_t latencyMs);
 
-    enum MeasurementMode {
+    enum MeasurementMode : int32_t {
         // Keep in sync with MEASUREMENT_MODE_... in
         // frameworks/base/media/java/android/media/audiofx/Visualizer.java
         NONE = 0x0,