Use Format_isValid() and Format_isEqual() instead of direct comparison

Change-Id: Ie87607aa514976947540a77775e6425c4e56e7d9
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 7126e92..28b9d77 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -239,7 +239,7 @@
                 dumpState->mSampleRate = sampleRate;
             }
 
-            if ((format != previousFormat) || (frameCount != previous->mFrameCount)) {
+            if ((!Format_isEqual(format, previousFormat)) || (frameCount != previous->mFrameCount)) {
                 // FIXME to avoid priority inversion, don't delete here
                 delete mixer;
                 mixer = NULL;