VolumeShaper: Make initialization consistent

Fix uninitialized enum variables for default
constructed aidl structs.

Test: compiles
Bug: 184662274
Change-Id: I5535dd6ce0648b4e02f64ce2b9ba10900d1e4b72
diff --git a/include/media/Interpolator.h b/include/media/Interpolator.h
index 2004acb..71e7604 100644
--- a/include/media/Interpolator.h
+++ b/include/media/Interpolator.h
@@ -43,7 +43,7 @@
     using InterpolatorType  = media::InterpolatorType;
 
     explicit Interpolator(
-            InterpolatorType interpolatorType = InterpolatorType::LINEAR,
+            InterpolatorType interpolatorType = InterpolatorType::CUBIC,
             bool cache = true)
         : mCache(cache)
         , mFirstSlope(0)