ACPI / APEI: Fix incorrect return value of ghes_proc()

Although ghes_proc() tests for errors while reading the error status,
it always return success (0). Fix this by propagating the return
value.

Fixes: d334a491

 (ACPI, APEI, Generic Hardware Error Source memory error support)
Signed-of-by: Punit Agrawal <punit.agrawa.@arm.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
[ rjw: Subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>