hwmon: (lm90) Fix sysfs and udev notifications

sysfs and udev notifications need to be sent to the _alarm
attributes, not to the value attributes.

Fixes: 94dbd23e

 ("hwmon: (lm90) Use hwmon_notify_event()")
Cc: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>