Get service by value instead of reference

to prevent a cleared service binder from being used.

Bug: 26040840
Change-Id: Ifb5483c55b172d3553deb80dbe27f2204b86ecdb

void MediaMetadataRetriever::DeathNotifier::binderDied(const wp<IBinder>& who __unused) {
 Mutex::Autolock lock(MediaMetadataRetriever::sServiceLock);
 MediaMetadataRetriever::sService.clear();
    ALOGW("MediaMetadataRetriever server died!");
}

void MediaMetadataRetriever::DeathNotifier::binderDied(const wp<IBinder>& who __unused) {
 Mutex::Autolock lock(MediaMetadataRetriever::sServiceLock);
 MediaMetadataRetriever::sService.clear();
    ALOGW("MediaMetadataRetriever server died!");
}
