selinux: fix misspellings using codespell tool

A typo is found out by codespell tool in 16th line of hashtab.c

$ codespell ./security/selinux/ss/
./hashtab.c:16: rouding  ==> rounding

Fix a typo found by codespell.
Signed-off-by: Xiong Zhenwu <xiong.zhenwu@zte.com.cn>
[PM: subject line tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/ss/hashtab.c

@@ -13,7 +13,7 @@ static struct kmem_cache *hashtab_node_cachep __ro_after_init;
 
 /*
  * Here we simply round the number of elements up to the nearest power of two.
- * I tried also other options like rouding down or rounding to the closest
+ * I tried also other options like rounding down or rounding to the closest
  * power of two (up or down based on which is closer), but I was unable to
  * find any significant difference in lookup/insert performance that would
  * justify switching to a different (less intuitive) formula. It could be that