During ghes_proc() we use ghes_ack_error() to tell an external agent
we are done with these records and it can re-use the memory.

rc may hold an error returned by ghes_read_estatus(), ENOENT causes
us to skip ghes_ack_error() (as there is nothing to ack), but rc may
also by EIO, which gets supressed.

ghes_clear_estatus() is where we mark the records as processed for
non GHESv2 error sources, and already spots the ENOENT case as
buf_paddr is set to 0 by ghes_read_estatus().

Move the ghes_ack_error() call in here to avoid extra logic with
the return code in ghes_proc().

This enables GHESv2 acking for NMI-like error sources. This is safe
as the buffer is pre-mapped by map_gen_v2() before the GHES is added
to any NMI handler lists.

This same pre-mapping step means we can't receive an error from
apei_read()/write() here as apei_check_gar() succeeded when it
was mapped, and the mapping was cached, so the address can't be
rejected at runtime. Remove the error-returns as this is now
called from a function with no return.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>