[PATCH] hwmon: Separate the lm90 register read function

Preparatory patch to add PEC support to the lm90 driver. We need a
centralized function to read register values, where the PEC code will
be later inserted. A positive side effect is that read errors are now
handled properly.

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