hammerhead: update max concurrent-instances limit.

Bug: 22603171
Change-Id: I1bd6790d702377d8ab6e78c37fef1631c4e10b78
diff --git a/media_codecs.xml b/media_codecs.xml
index 3b8cc5d..8767066 100644
--- a/media_codecs.xml
+++ b/media_codecs.xml
@@ -87,7 +87,7 @@
             <Limit name="bitrate" range="1-100000000" />
             <Feature name="adaptive-playback" />
             <Feature name="secure-playback" required="true" />
-            <Limit name="concurrent-instances" max="4" />
+            <Limit name="concurrent-instances" max="6" />
         </MediaCodec>
         <MediaCodec name="OMX.qcom.video.decoder.mpeg4" type="video/mp4v-es" >
             <Quirk name="requires-allocate-on-input-ports" />