Change sprintf format string from %zu to %i

The resulting string became wrong on Windows. Instead of printing
the numerical value in number_of_streams_, the string "zu" got
printed. (Linux and Mac worked fine already.)

This will result in a change of statistics name in the performance
graphs.

R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/10569005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5776 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed