Include missing header.

This should fix the building error on the buildbot.

Review URL: http://codereview.chromium.org/668100
diff --git a/utils/kernel_utility.cc b/utils/kernel_utility.cc
index 4a90d3c..4e12c6d 100644
--- a/utils/kernel_utility.cc
+++ b/utils/kernel_utility.cc
@@ -9,6 +9,7 @@
 
 #include <errno.h>
 #include <getopt.h>
+#include <stdio.h>
 #include <stdint.h>  // Needed for UINT16_MAX.
 #include <stdlib.h>
 #include <unistd.h>