apparmor: Fix kernel-doc warnings in apparmor/capability.c

Fix kernel-doc warnings:

security/apparmor/capability.c:45: warning: Function parameter
or member 'ab' not described in 'audit_cb'
security/apparmor/capability.c:45: warning: Function parameter
or member 'va' not described in 'audit_cb'

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>