selinux: fix misspellings using codespell tool

A typo is f out by codespell tool in 422th line of security.h:

$ codespell ./security/selinux/include/
./security.h:422: thie  ==> the, this

Fix a typo found by codespell.

Signed-off-by: Xiong Zhenwu <xiong.zhenwu@zte.com.cn>
[PM: subject line tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>