hwmon: (tmp102) Fix suspend and resume functions

Suspend and resume functions shouldn't overwrite the configuration
register. They should only alter the one bit they have to touch.

Also don't assume that register reads and writes always succeed.
Handle errors properly, shall they happen.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Steven King <sfking@fdwdc.com>