Speed up SimpleDecodingSource

SimpleDecodingSource was waiting up to 5 milliseconds for each input
buffer, when it should not have been waiting at all, and instead
just check if there's an output buffer. This greatly increases
throughput for files with small buffers such as audio files, e.g.
a 6x speedup was observed for ogg and mp3 test streams.

Test: stagefright
Change-Id: If9fc91b823442926e8452d0e6cf95735b7248596

media/libstagefright/SimpleDecodingSource.cpp

@@ -36,7 +36,7 @@
 using namespace android;
 
 const int64_t kTimeoutWaitForOutputUs = 500000; // 0.5 seconds
-const int64_t kTimeoutWaitForInputUs = 5000; // 5 milliseconds
+const int64_t kTimeoutWaitForInputUs = 0; // don't wait
 const int kTimeoutMaxRetries = 20;
 
 //static