hwmon: (it87) Fix in7 on IT8720F

The IT8720F has no VIN7 pin, so VCCH should always be routed
internally to VIN7 with an internal divider. Curiously, there still
is a configuration bit to control this, which means it can be set
incorrectly. And even more curiously, many boards out there are
improperly configured, even though the IT8720F datasheet claims that
the internal routing of VCCH to VIN7 is the default setting. So we
force the internal routing in this case.

It turns out that all boards with the wrong setting are from Gigabyte,
so I suspect a BIOS bug. But it's easy enough to workaround in the
driver, so let's do it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Jean-Marc Spaggiari <jean-marc@spaggiari.org>
Cc: stable@kernel.org