cgroup: Fix cgroup_can_fork() and cgroup_post_fork() kernel-doc comment

Add the description of @kargs in cgroup_can_fork() and
cgroup_post_fork() kernel-doc comment to remove warnings found
by running scripts/kernel-doc, which is caused by using 'make W=1'.

kernel/cgroup/cgroup.c:6235: warning: Function parameter or member
'kargs' not described in 'cgroup_can_fork'
kernel/cgroup/cgroup.c:6296: warning: Function parameter or member
'kargs' not described in 'cgroup_post_fork'
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -6224,6 +6224,7 @@ static void cgroup_css_set_put_fork(struct kernel_clone_args *kargs)
 /**
  * cgroup_can_fork - called on a new task before the process is exposed
  * @child: the child process
+ * @kargs: the arguments passed to create the child process
  *
  * This prepares a new css_set for the child process which the child will
  * be attached to in cgroup_post_fork().
@@ -6286,6 +6287,7 @@ void cgroup_cancel_fork(struct task_struct *child,
 /**
  * cgroup_post_fork - finalize cgroup setup for the child process
  * @child: the child process
+ * @kargs: the arguments passed to create the child process
  *
  * Attach the child process to its css_set calling the subsystem fork()
  * callbacks.