hwmon: (occ) Prevent sysfs error attribute from returning error

The error sysfs attribute returns the stored error state of the OCC and
doesn't depend on the OCC poll response. Therefore, split the error
attribute into it's own function to avoid failing out of the function if
the poll response fails.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>