hwmon: Let w83781d and lm78 load again

Let the w83781d and lm78 hardware monitoring drivers load even when
no chip was detected at the ISA address. There can still be supported
chips connected to an I2C bus or SMBus.

This fixes bug #7293.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>