util: Fix build of LinkNode.java.

If you compile with JDK 1.7 you get the following error:

mNext has private access in LinkedNode
return T node.mNext == mHead ? null : node.mNext;

Change-Id: Ic1e60f76461da3e75b4ca8402622251e63569beb
Merge branch 'Cyanogen/cm-11.0'