freebsd build error (19)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: de701f9bdbe0 MAC/do: Apply a rule on real UID/GID instead ..
git tree: freebsd-src
console output: https://syzkaller.appspot.com/x/log.txt?x=16ed34f8580000
dashboard link: https://syzkaller.appspot.com/bug?extid=273e5fe9fd6534b4792f

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+273e5f...@syzkaller.appspotmail.com

sys/sys/refcount.h:69:26: error: passing 'const volatile u_int *' (aka 'const volatile unsigned int *') to parameter of type 'volatile u_int *' (aka 'volatile unsigned int *') discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]

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