Preprocessing: Use free() for session->outBuf

Bug: 182575590
Test: AudioPreProcessingTest on host

Change-Id: I5e72528651c1e36dc3f10101c24dc8b42e69f13d
diff --git a/media/libeffects/preprocessing/PreProcessing.cpp b/media/libeffects/preprocessing/PreProcessing.cpp
index 03ccc34..e8ae58e 100644
--- a/media/libeffects/preprocessing/PreProcessing.cpp
+++ b/media/libeffects/preprocessing/PreProcessing.cpp
@@ -910,7 +910,7 @@
         session->apm = NULL;
         delete session->inBuf;
         session->inBuf = NULL;
-        delete session->outBuf;
+        free(session->outBuf);
         session->outBuf = NULL;
         delete session->revBuf;
         session->revBuf = NULL;