Neon version of ScaleErrorSignal()

The performance gain on a Nexus 7 reported by audioproc is ~4.7%

The output is NOT bit exact. Any difference seen is +-1.

BUG=3131
R=bjornv@webrtc.org, cd@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12779004

Patch from Scott LaVarnway <slavarnw@gmail.com>.

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6529 4adac7df-926f-26a2-2b94-8c16560cd09d