ACPI / debugger: copy_to_user doesn't return errors

The copy_to/from_user() functions don't return error codes, they return
the number of bytes remaining.  We had intended to return -EFUALT here.
We actually have already checked access_ok() in an earlier function so
I don't think these functions will fail but let's fix it anyway.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>