ACPI/APEI: Clear GHES block_status before panic()

In __ghes_panic() clear the block status in the APEI generic
error status block for that generic hardware error source before
calling panic() to prevent a second panic() in the crash kernel
for exactly the same fatal error.

Otherwise ghes_probe(), running in the crash kernel, would see
an unhandled error in the APEI generic error status block and
panic again, thereby precluding any crash dump.

Signed-off-by: Lenny Szubowicz <lszubowi@redhat.com>
Signed-off-by: David Arcari <darcari@redhat.com>
Tested-by: Tyler Baicar <baicar.tyler@gmail.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>