Use inclusive term in AudioTrackSurroundTest

Rename "m*sterBuffer" to "mainBuffer"

Test: m
Change-Id: I5a838f594365445dc40b1b4de9862497b97a3bc2
diff --git a/tests/tests/media/src/android/media/cts/AudioTrackSurroundTest.java b/tests/tests/media/src/android/media/cts/AudioTrackSurroundTest.java
index 7908826..8425672 100644
--- a/tests/tests/media/src/android/media/cts/AudioTrackSurroundTest.java
+++ b/tests/tests/media/src/android/media/cts/AudioTrackSurroundTest.java
@@ -185,11 +185,11 @@
         ShortBuffer shortBuffer =
                 ByteBuffer.wrap(byteBuffer).order(ByteOrder.LITTLE_ENDIAN).asShortBuffer();
         // Unfortunately, ShortBuffer.array() works with allocated buffers only.
-        short[] masterBuffer = new short[byteBuffer.length / 2];
-        for (int i = 0; i < masterBuffer.length; i++) {
-            masterBuffer[i] = shortBuffer.get();
+        short[] mainBuffer = new short[byteBuffer.length / 2];
+        for (int i = 0; i < mainBuffer.length; i++) {
+            mainBuffer[i] = shortBuffer.get();
         }
-        return masterBuffer;
+        return mainBuffer;
     }
 
     public void testLoadSineSweep() throws Exception {