hwmon: fix lm78 detection regression

Here is a small but important bugfix to the lm78 driver. I found out about this
problem because a Fedora user filed a bug that the lm78 driver no longer worked
on his system: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=249428

The problem is that sometime ago the isa lm78 detection was made more stringent
and this new code now checks the chip-id, but does not accept a chip-id of 20h,
however a chip-id of 20h is valid, and is excepted in the main probe function
of the driver, see line 551. This fixed also makes the isa detection code
accept the chip-id of 0x20 fixing this issue.

Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>