[WATCHDOG] ibmasr: remove unnecessary spin_unlock()

__asr_toggle() is always called with asr_lock held.
But there is unnecessary spin_unlock() call in __asr_toggle().

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Acked-by: Andrey Panin <pazke@donpac.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>