i2c-nforce2: Disable the second SMBus channel on the DFI Lanparty NF4 Expert

There is a strange chip at 0x2e on the second SMBus channel of the
DFI Lanparty NF4 Expert motherboard. Accessing the chip reboots the
system. As there's nothing interesting on this SMBus channel, the
easiest and safest thing to do is to disable it on that board.

This is a better fix to bug #5889 than the it87 driver update that was
done originally:
http://bugzilla.kernel.org/show_bug.cgi?id=5889

Signed-off-by: Jean Delvare <khali@linux-fr.org>