mm/memory_hotplug: Do not unlock when fails to take the device_hotplug_lock

mm/memory_hotplug: Do not unlock when fails to take the device_hotplug_lock

When adding the memory by probing memory block in sysfs interface, there is an
obvious issue that we will unlock the device_hotplug_lock when fails to takes it.

That issue was introduced in Commit 6c615b6bae48
("mm/memory_hotplug: make add_memory() take the device_hotplug_lock")

We should drop out in time when fails to take the device_hotplug_lock.

Fixes: 6c615b6bae48 ("mm/memory_hotplug: make add_memory() take the device_hotplug_lock")
Reported-by: Yang yingliang <yangyingliang@huawei.com>
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>