i2c: i801: fix DNV's SMBCTRL register offset

DNV's iTCO is slightly different with SMBCTRL sitting at a different
offset when compared to all other devices. Let's fix so that we can
properly use iTCO watchdog.

Fixes: 84d7f2eb ("i2c: i801: Add support for Intel DNV")
Cc: <stable@vger.kernel.org> # v4.4+
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>