Fixed warning about invalid format string.
Fixed warning about invalid format string.

Summary:
Code was trying to print a uint32_t with %zd, which is ssize_t.
Fixed it to use %u.

Reviewed By: bertmaher

Differential Revision: D3335359

fbshipit-source-id: cc919500e6ea8d90cfe33026790ccc022037cdb7

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex