MIDI render thread was nice 0, should be nice -16.

Seems like a recent change sets the thread priority to 0. Previously it
inherited priority from the parent thread. This change sets the MIDI
render thread priority to the default for audio threads.
Reference bug 1800905

media/libmediaplayerservice/MidiFile.cpp

@@ -89,7 +89,7 @@ MidiFile::MidiFile() :
     // create playback thread
     {
         Mutex::Autolock l(mMutex);
-        createThreadEtc(renderThread, this, "midithread");
+        createThreadEtc(renderThread, this, "midithread", ANDROID_PRIORITY_AUDIO);
         mCondition.wait(mMutex);
         LOGV("thread started");
     }