apparmor: Fix some kernel-doc comments

Fix some kernel-doc comments to silence the warnings:
security/apparmor/policy.c:117: warning: Function parameter or member 'kref' not described in 'aa_pdb_free_kref'
security/apparmor/policy.c:117: warning: Excess function parameter 'kr' description in 'aa_pdb_free_kref'
security/apparmor/policy.c:882: warning: Function parameter or member 'subj_cred' not described in 'aa_may_manage_policy'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=7037


Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>