Fix an ambiguous call to pow() error.
Fix an ambiguous call to pow() error.

Switch to powf() and explicitly define the second parameter as float.
Review URL: http://webrtc-codereview.appspot.com/89006

git-svn-id: 9b397c5dfe384c04b1b200d5305b653241000171@269 4adac7df-926f-26a2-2b94-8c16560cd09d

lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override