eeepc-laptop: store_cpufv: return error if set_acpi fails

The result of set_acpi is left unchecked, but it may return errors. If
one occurs, send the error to the caller. There's no reason to lie about
it, if set_acpi fails.

Signed-off-by: Frans Klaver <fransklaver@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>