Fix cpplint errors in audio_processing.h

TBR=leozwang@webrtc.org
BUG=1114

Review URL: https://webrtc-codereview.appspot.com/934015

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3108 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed