hwmon: (it87) Ensure that pwm control cache is current before updating values

hwmon: (it87) Ensure that pwm control cache is current before updating values

BugLink: http://bugs.launchpad.net/bugs/1672544
commit 82dbe987b70042b340f851bdc969a971081e5f02 upstream.

If sensor attributes were never read, the pwm control data has not been
initiialized, which can cause wrong driver behavior. Ensure that cached
data is current before acting on it.

Reported-by: Kevin Folz <kfolz@evertz.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>