ACPI / battery: Fix doubly added battery on system suspend

Commit 297d716f ("power_supply: Change ownership from driver to
core") inverted the logic in battery_notify().  As an effect already
present battery was re-added on each system suspend or hibernation.

    WARNING: CPU: 0 PID: 303 at ../fs/sysfs/dir.c:31 sysfs_warn_dup+0x68/0x80()
    sysfs: cannot create duplicate filename '/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A03:00/PNP0C0A:00/power_supply/BAT0'
    CPU: 0 PID: 303 Comm: rtcwake Not tainted 4.0.0-ARCH-02621-g07e6253af953 #48
    Call Trace:
      sysfs_create_dir_ns+0x8d/0xa0
      kobject_add_internal+0xb6/0x370
      kobject_add+0x6f/0xd0
      device_add+0x120/0x6c0
      __power_supply_register+0x145/0x290
      power_supply_register_no_ws+0x10/0x20
      sysfs_add_battery+0x84/0xc5 [battery]
      battery_notify+0x45/0x6b [battery]
      notifier_call_chain+0x4f/0x80
      __blocking_notifier_call_chain+0x4b/0x70
      blocking_notifier_call_chain+0x16/0x20
      pm_notifier_call_chain+0x1a/0x40
      pm_suspend+0x3ed/0x4e0

Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-By: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>