hwmon: (w83795) Delay reading limit registers

Wait until we need the limit register values, instead of pre-reading
them. This saves 544 ms on modprobe on my test system. Obviously this
time is added when first running "sensors" or any other monitoring
application, but I think it is better than slowing down the boot.

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