ACPI: NFIT: Fix comparison to '-ENXIO'

Initial value of rc is '-ENXIO', and we should
use the initial value to check it.

Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>