sysfs: handle duplicate removal attempts in sysfs_remove_group()

Commit bcdde7e2 (sysfs: make __sysfs_remove_dir() recursive) changed
the behavior so that directory removals will be done recursively. This
means that the sysfs group might already be removed if its parent directory
has been removed.

The current code outputs warnings similar to following log snippet when it
detects that there is no group for the given kobject:

 WARNING: CPU: 0 PID: 4 at fs/sysfs/group.c:214 sysfs_remove_group+0xc6/0xd0()
 sysfs group ffffffff81c6f1e0 not found for kobject 'host7'
 Modules linked in:
 CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted 3.12.0+ #13
 Hardware name:                  /D33217CK, BIOS GKPPT10H.86A.0042.2013.0422.1439 04/22/2013
 Workqueue: kacpi_hotplug acpi_hotplug_work_fn
  0000000000000009 ffff8801002459b0 ffffffff817daab1 ffff8801002459f8
  ffff8801002459e8 ffffffff810436b8 0000000000000000 ffffffff81c6f1e0
  ffff88006d440358 ffff88006d440188 ffff88006e8b4c28 ffff880100245a48
 Call Trace:
  [<ffffffff817daab1>] dump_stack+0x45/0x56
  [<ffffffff810436b8>] warn_slowpath_common+0x78/0xa0
  [<ffffffff81043727>] warn_slowpath_fmt+0x47/0x50
  [<ffffffff811ad319>] ? sysfs_get_dirent_ns+0x49/0x70
  [<ffffffff811ae526>] sysfs_remove_group+0xc6/0xd0
  [<ffffffff81432f7e>] dpm_sysfs_remove+0x3e/0x50
  [<ffffffff8142a0d0>] device_del+0x40/0x1b0
  [<ffffffff8142a24d>] device_unregister+0xd/0x20
  [<ffffffff8144131a>] scsi_remove_host+0xba/0x110
  [<ffffffff8145f526>] ata_host_detach+0xc6/0x100
  [<ffffffff8145f578>] ata_pci_remove_one+0x18/0x20
  [<ffffffff812e8f48>] pci_device_remove+0x28/0x60
  [<ffffffff8142d854>] __device_release_driver+0x64/0xd0
  [<ffffffff8142d8de>] device_release_driver+0x1e/0x30
  [<ffffffff8142d257>] bus_remove_device+0xf7/0x140
  [<ffffffff8142a1b1>] device_del+0x121/0x1b0
  [<ffffffff812e43d4>] pci_stop_bus_device+0x94/0xa0
  [<ffffffff812e437b>] pci_stop_bus_device+0x3b/0xa0
  [<ffffffff812e437b>] pci_stop_bus_device+0x3b/0xa0
  [<ffffffff812e44dd>] pci_stop_and_remove_bus_device+0xd/0x20
  [<ffffffff812fc743>] trim_stale_devices+0x73/0xe0
  [<ffffffff812fc78b>] trim_stale_devices+0xbb/0xe0
  [<ffffffff812fc78b>] trim_stale_devices+0xbb/0xe0
  [<ffffffff812fcb6e>] acpiphp_check_bridge+0x7e/0xd0
  [<ffffffff812fd90d>] hotplug_event+0xcd/0x160
  [<ffffffff812fd9c5>] hotplug_event_work+0x25/0x60
  [<ffffffff81316749>] acpi_hotplug_work_fn+0x17/0x22
  [<ffffffff8105cf3a>] process_one_work+0x17a/0x430
  [<ffffffff8105db29>] worker_thread+0x119/0x390
  [<ffffffff8105da10>] ? manage_workers.isra.25+0x2a0/0x2a0
  [<ffffffff81063a5d>] kthread+0xcd/0xf0
  [<ffffffff81063990>] ? kthread_create_on_node+0x180/0x180
  [<ffffffff817eb33c>] ret_from_fork+0x7c/0xb0
  [<ffffffff81063990>] ? kthread_create_on_node+0x180/0x180

On this particular machine I see ~16 of these message during Thunderbolt
hot-unplug.

Fix this in similar way that was done for sysfs_remove_one() by checking
if the parent directory has already been removed and bailing out early.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>