ACPI / APEI: Don't update struct ghes' flags in read/clear estatus

ghes_read_estatus() sets a flag in struct ghes if the buffer of
CPER records needs to be cleared once the records have been
processed. This flag value is a problem if a struct ghes can be
processed concurrently, as happens at probe time if an NMI arrives
for the same error source. The NMI clears the flag, meaning the
interrupted handler may never do the ghes_estatus_clear() work.

The GHES_TO_CLEAR flags is only set at the same time as
buffer_paddr, which is now owned by the caller and passed to
ghes_clear_estatus(). Use this value as the flag.

A non-zero buf_paddr returned by ghes_read_estatus() means
ghes_clear_estatus() should clear this address. ghes_read_estatus()
already checks for a read of error_status_address being zero,
so CPER records cannot be written here.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>