hwmon: (lm90) Use worker for alarm notifications

Reporting alarms using hwmon_notify_event() may result in a callback
from the thermal subsystem. This means that such notifications must
not hold the update lock to avoid a deadlock. To avoid this situation,
use a worker to handle notifications.

Reported-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Fixes: f6d07751

 ("hwmon: (lm90) Rework alarm/status handling")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>