hwmon/w83793: Remove the description of AMDSI and update the voltage formula

Fix the driver to match the information in datasheet 1.0. AMD 
SI interface is marked as reserved, computing formula for 5VDD
and 5VSB is updated.

Signed-off-by: Gong Jun <jgong@winbond.com>
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>