cgroups: remove some redundant NULL checks
cgroups: remove some redundant NULL checks

- In cgroup_clone(), if vfs_mkdir() returns successfully,
  dentry->d_fsdata will be the pointer to the newly created
  cgroup and won't be NULL.

- a cgroup file's dentry->d_fsdata won't be NULL, guaranteed
  by cgroup_add_file().

- When walking through the subsystems of a cgroup_fs (using
  for_each_subsys), cgrp->subsys[ss->subsys_id] won't be NULL,
  guaranteed by cgroup_create().

(Also remove 2 unused variables in cgroup_rmdir().

Signed-off-by: Li Zefan <5dc16b054e85ffba6c8d314d8e55ae95dcab12a5@cn.fujitsu.com>
Cc: Paul Menage <a4e32ff3ad614f63c49bddfcf4b7598c6857b687@google.com>
Cc: KAMEZAWA Hiroyuki <634f508bd7c47cf0ee4126243675c3e598920fbc@jp.fujitsu.com>
Cc: Balbir Singh <65a1aed538f36fed73d8c45e9ddfc585ce9f4abf@in.ibm.com>
Cc: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@openvz.org>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas