Fix bug in test-resample's AudioBufferProvider

The contract for AudioBufferProvider::releaseBuffer() was missing.

Bug: 12194314
Change-Id: I2fcf75e7b8eaf6db34f360206d79457a04a73565
diff --git a/services/audioflinger/test-resample.cpp b/services/audioflinger/test-resample.cpp
index 0d00a0f..403bb6d 100644
--- a/services/audioflinger/test-resample.cpp
+++ b/services/audioflinger/test-resample.cpp
@@ -202,6 +202,8 @@
                 mNextFrame += buffer->frameCount;
                 mUnrel -= buffer->frameCount;
             }
+            buffer->frameCount = 0;
+            buffer->i16 = NULL;
         }
     } provider(input_vaddr, input_size, channels);