selinux: avoid printk_ratelimit()

The usage of printk_ratelimit() is discouraged, see
include/linux/printk.h, thus use pr_warn_ratelimited().

While editing this line address the following checkpatch warning:

    WARNING: Integer promotion: Using 'h' in '%hu' is unnecessary

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>