selftests/x86: fix printk warnings reported by clang

These warnings are all of the form, "the format specified a short
(signed or unsigned) int, but the value is a full length int".

Acked-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>