x86/mce: Fix regression. All error records should report via /dev/mcelog

I'm getting complaints from validation teams that have updated their
Linux kernels from ancient versions to current. They don't see the
error logs they expect. I tell the to unload any EDAC drivers[1], and
things start working again.  The problem is that we short-circuit
the logging process if any function on the decoder chain claims to
have dealt with the problem:

	ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
	if (ret == NOTIFY_STOP)
		return;

The logic we used when we added this code was that we did not want
to confuse users with double reports of the same error.

But it turns out users are not confused - they are upset that they
don't see a log where their tools used to find a log.

I could also get into a long description of how the consumer of this
log does more than just decode model specific details of the error.
It keeps counts, tracks thresholds, takes actions and runs scripts
that can alert administrators to problems.

[1] We've recently compounded the problem because the acpi_extlog
driver also registers for this notifier and also returns NOTIFY_STOP.

Signed-off-by: Tony Luck <tony.luck@intel.com>