selinux: annotate false positive data race to avoid KCSAN warnings

KCSAN flags the check of isec->initialized by
__inode_security_revalidate() as a data race. This is indeed a racy
check, but inode_doinit_with_dentry() will recheck with isec->lock held.
Annotate the check with the data_race() macro to silence the KCSAN false
positive.

Reported-by:  <syzbot+319ed1769c0078257262@syzkaller.appspotmail.com>
Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>