media: use size_t for integer iterator to Vector::size()

Change-Id: I0a744dc7815a86a993df9b0623440be620ec8903
diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 26dac95..c0c34f7 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -525,7 +525,7 @@
         }
 
         // Look for sync events awaiting for a session to be used.
-        for (int i = 0; i < (int)mPendingSyncEvents.size(); i++) {
+        for (size_t i = 0; i < mPendingSyncEvents.size(); i++) {
             if (mPendingSyncEvents[i]->triggerSession() == lSessionId) {
                 if (thread->isValidSyncEvent(mPendingSyncEvents[i])) {
                     if (lStatus == NO_ERROR) {
@@ -831,7 +831,7 @@
 
     AutoMutex lock(mLock);
     mStreamTypes[stream].mute = muted;
-    for (uint32_t i = 0; i < mPlaybackThreads.size(); i++)
+    for (size_t i = 0; i < mPlaybackThreads.size(); i++)
         mPlaybackThreads.valueAt(i)->setStreamMute(stream, muted);
 
     return NO_ERROR;