ACPI / device_sysfs: Change _SUN and _STA show functions error return to EIO

The error return from a sysfs show function is passed up through
the call chain and visible as the return from the read system call.
The show functions for the _STA and _SUN object currently return
-ENODEV. This patch changes the return to -EIO. ENODEV makes less
sense since the "device' exists or there wouldn't be a sysfs file.

Signed-off-by: Betty Dall <betty.dall@hpe.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>