Add missing cstdio include

This fixes a build error where std::fprintf can't be found.

Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Change-Id: Ie22697732ae8b51e58ec5d5c907cc4839d5dc892
diff --git a/i2c.cpp b/i2c.cpp
index ff5a66b..546a872 100644
--- a/i2c.cpp
+++ b/i2c.cpp
@@ -24,6 +24,7 @@
 
 #include <array>
 #include <cerrno>
+#include <cstdio>
 #include <cstring>
 #include <ipmid/iana.hpp>
 #include <ipmid/oemopenbmc.hpp>