LiveSession: fix incorrect stream key (subtitle"s")

Bug: 13402087
Change-Id: Ic46e3069c6e41f90ead47cae84cbe0123d11002a
diff --git a/media/libstagefright/httplive/LiveSession.cpp b/media/libstagefright/httplive/LiveSession.cpp
index c1c3e2b..3e11759 100644
--- a/media/libstagefright/httplive/LiveSession.cpp
+++ b/media/libstagefright/httplive/LiveSession.cpp
@@ -75,7 +75,7 @@
 
     mStreams[kAudioIndex] = StreamItem("audio");
     mStreams[kVideoIndex] = StreamItem("video");
-    mStreams[kSubtitleIndex] = StreamItem("subtitle");
+    mStreams[kSubtitleIndex] = StreamItem("subtitles");
 
     for (size_t i = 0; i < kMaxStreams; ++i) {
         mPacketSources.add(indexToType(i), new AnotherPacketSource(NULL /* meta */));