drmserver: add group drm

Make the drm server run as UID=drm, GID=drm. This ensures that
any files created by the drmserver app do not have GID=system.

Bug: 5834297
Change-Id: I3409ad350e9cc82bb0982cdbe470ec1f10b1ca67
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 17374f0..c445f8e 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -438,7 +438,7 @@
 service drm /system/bin/drmserver
     class main
     user drm
-    group system inet drmrpc
+    group drm system inet drmrpc
 
 service media /system/bin/mediaserver
     class main