qga: Fix two format strings for MinGW

Both code locations cause a compiler warning. Using "%s" instead of "%lu"
would result in a program crash if the wrong code were executed.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1385409257-2522-1-git-send-email-sw@weilnetz.de
Signed-off-by: Anthony Liguori <aliguori@amazon.com>
