hwmon: (it87) Avoid registering the same chip on both SIO addresses

commit 8358378b22518d92424597503d3c1cd302a490b6 upstream.

IT8705F is known to respond on both SIO addresses. Registering it twice
may result in system lockups.

Reported-by: Russell King <linux@armlinux.org.uk>
Fixes: e84bd953 ("hwmon: (it87) Add support for second Super-IO chip")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>