Minor style cleanups.

A few changes to demonstrate a slightly cleaner way to write
JNI code in the framework especially when multiple types are
involved.  We use this pattern in many other places outside
of the media stack.

Added more detail to the UnsupportedOperationException that
occurs when buffer formats don't match.

Change-Id: Ic894dc1bd71b387f1be6ea1798fa59e533e9574f